[Kelli]

I recently got this truck 2002 GMC Sierra 2500 HD 8.1 vortec motor Allison 1000 transmission... When I first got it they told me it was stuck in tow mode that I had to get it out of tow mode. Now it seems to be stuck in third gear the original Alisson I had in there would drive correctly in the mornings for about an hour going through all the gears then it would get stuck in third. So I purchased another used Allison transmission and put it in there and upon turning on the vehicle and going about one inch it goes clunk clunk and shifts into third and get stuck there. I spoke with the transmission person that says there's no way in hell the two transmissions are going to do the exact same thing and that it's probably either a wiring issue (which would explain the tow mode from the videos I've seen) or a computer brain issue but however it could be a transmission issue I'm not sure. I am not a mechanic I just know what I've been told about this this has been going on for the past oh 30 days and now I don't know should I take it to a transmission specialist or just a mechanic that does transmissions and wiring and whatever else might be the problem I need some help on what to do. I paid $3,500 for the truck I paid another two grand for the second transmission I paid the mechanic who switched out the transmissions another two grand and I've driven the truck maybe 3 days I don't have a lot of more money so I need to know the most economical place I can take this that is going to give me the right information and fix my truck

 

[Kelli]

About a month and a half ago I purchased a 2002 GMC Sierra 2500 HD was it 8.1 vortec motor and an Allison 1000 transmission. I was told that it was stuck in tow mode when I first got it. But now it's stuck in third gear. When I would first start driving the truck in the morning it would shift normally through the gears and after about an hour or so it would get stuck in third if I shut it off for a little while let it cool off or whatever it would do the same thing like it says in the morning. Mechanic said it was stuck in limp mode that I needed a new transmission so I purchased for $2,000 a rebuilt Allison transmission. Put he put that one in my truck and now I start the truck and it immediately shifts into third gear and gets stuck. I talked to another transmission person who said that there's no way in hell those two transmissions are going to do the same exact thing and be stuck in third gear that it's probably either a problem with the wiring (which would explain the video I saw when I was trying to figure out what tow mode was) or a problem with the computer brain telling it to get stuck in third gear. I am not a mechanic and I don't even know where to take my truck do I take it to a transmission specialist is it a transmission problem? Or do I take it to a mechanic who does both because it could be the wiring and it could be the brain? I don't even know where to take my truck all I know is the truck cost me $3,500 the second Allison transmission cost me two grand and I had to pay the mechanic $2,000 also and I've driven the truck maybe 3 days. If anyone can give me some ideas or help I mean there is more information if you have any questions that I could pass on if you can help in any way I don't know what to do

 

[nealinator]

What did the shop that swapped the trans say? I assume they diagnosed this and suggested it and that didn’t work? So they should be explaining to you why a professional shop Mia diagnosed the problem and cost you $4k. Or did the transaction go down in a different way?

 

[Kelli]

He said he was at a loss. And I think he was actually just tired of working on my truck. So now the original transmission that would drive right for an hour and then going to third is in the back of my truck and the second one I bought is in the truck and it clunks hard and shifts into third gear immediately. The mechanic charged me for putting for taking out one transmission and putting in another transmission and then said he's not sure what the problem is cuz it wasn't fixed when he did that

 

[Kelli]

He said he was at a loss. And I think he was actually just tired of working on my truck. So now the original transmission that would drive right for an hour and then going to third is in the back of my truck and the second one I bought is in the truck and it clunks hard and shifts into third gear immediately. The mechanic charged me for putting for taking out one transmission and putting in another transmission and then said he's not sure what the problem is cuz it wasn't fixed when he did that

Oh and he also gave me a piece of paper with some transmission codes on it that the one that's in the truck now that just shifts immediately into third year was throwing but the one that's in the back of the truck was only throwing 1 code

 

[davester3500]

Paragraphs, they are your friend. It sucks to read big blocks of text like you produced.

It sounds like you need to find better mechanics.

The T/H thing should be relatively easy to determine if the probelm is between the button and the bcm, or the bcm elsewhere. Something like a tech ii (or a similar, more advanced computer setup that any decent mechanic will have) will show if the ecm/tcm things it's in tow/haul mode, and be able to command it on & off to see what happens, and see what the tcm is doing as you drive around (to figure out why it stays in 3rd gear).

 

[Kelli]

Paragraphs, they are your friend. It sucks to read big blocks of text like you produced.

It sounds like you need to find better mechanics.

The T/H thing should be relatively easy to determine if the probelm is between the button and the bcm, or the bcm elsewhere. Something like a tech ii (or a similar, more advanced computer setup that any decent mechanic will have) will show if the ecm/tcm things it's in tow/haul mode, and be able to command it on & off to see what happens, and see what the tcm is doing as you drive around (to figure out why it stays in 3rd gear).

 

[Kelli]

So then I should take it to a transmission specialist yes?

 

[davester3500]

Probably. That person would be able to give you a better understanding of what could be wrong, and what it would take to fix it.

 

[Kelli]

Probably. That person would be able to give you a better understanding of what could be wrong, and what it would take to fix it.

Thanks for the input. I appreciate it

 

[PTR]

3rd gear, I believe, is limp mode.

 

[nealinator]

I am still not following how this repair went down. Did you take it to a transmission place, ask them to repair your truck and this is what happened? Or did you determine yourself that you needed a transmission, purchased it yourself, brought it to someone and ask them to swap it for you? There is a big difference potentially in who is responsible based on how this went down.

 

[nealinator]

Seems you have two posts with the same question going on here.

Allison 1000 issue. Maybe??

I recently got this truck 2002 GMC Sierra 2500 HD 8.1 vortec motor Allison 1000 transmission... When I first got it they told me it was stuck in tow mode that I had to get it out of tow mode. Now it seems to be stuck in third gear the original Alisson I had in there would drive correctly in the...

www.silveradosierra.com

 

[B52Bombardier1]

What are those transmission codes on the piece of paper? They would tell us a lot. I believe you might have more than one problem here. Possibly wiring, bad PCM / TCM and different problems organically in both of these candidate transmissions.

Rick

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