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Hi. I own a 93 GMC Sierra (LWB) 4.3L. Everything in the truck is stock. The problem is, no matter how long I allow the truck to warm up, it is shifting very hard from first to second gear. All the rest shift fine throughout the driving range. Any idea's? Thanks
 

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Sometimes that could be caused by valve body wear, or the separator plate being worn. A hard shift, but solid without slips probably means the packs etc are ok. Might not need a new transmission, just some work done to that valve body.
 

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Which transmission is it? My '03 with the 4L60-E (if memory serves) had the same problems at around 143,000 miles and when it was taken to a shop, all of the clutch packs had been worn down to resemble the cardboard backing on a notepad. The shop owner went ahead and installed the guts out of a 1-ton's transmission which doubled the amount of clutch packs and increased the thickness as well. If that's what has happened to your truck it might not be a bad idea to have them do the same thing, especially if you pull trailers a lot like I do.
 

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I've reaseached this topic , sometimes it is the TPS sensor sending wrong shift data to trans , mine does it when warmed up after a highway run when I slow down and shift from 1 to 2 , it's also intermintent sometimes it does it , and when cold it doesn't do it , just ordered a throttle body since my sensor is built in .
2007 sliveraldo 4L60E 4.8L 4X4
 

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My 2015 GMC will do it till the trans warms up a bit. Second gear is kinda hard but not bad and it flares third gear like it will let go from second into third. After the first drive it's normal. It can sit for 30min and do it again. Fluid look ok pan was clean magnet was normal. Soo idk people say it's a normal thing for these trucks
 

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GM says that the 2-3 flare is 'normal'. My '13 does it, too.

Document ID: 4597361

Some customers may comment on a 2-3 upshift slip or flare.

This condition is a NORMAL characteristic of the transmission
and will not cause durability concerns and no repair attempts should
be made.


Service Procedure
At this time this flare condition has been recognized in two different driving conditions:
1. During the first 2-3 upshift after the vehicle has been sitting, engine off for several hours. This
condition may be caused by air that is trapped in the 3-S-R clutch assembly.
When the first 2-3 upshift is made this trapped air is purged and the following 2-3 shifts will
be normal with no flare.
When diagnosing this condition, a garage shift into reverse before drive will purge this air and
prevent the 2-3 flare from occurring. This condition is a NORMAL characteristic of the
transmission, it will not cause durability concerns and no repair attempts should be made.
2. When transmission ATF temperature is at or below 85 degrees F (30 degrees C). This 2-3
upshift flare can occur until the ATF temperature warms. If the 2-3 flare is determined to be
ATF temperature sensitive use a Tech 2 to make note of the throttle position when the flare
occurs. Drive the vehicle to get ATF temperature to at least 104 degrees F (40 degrees C) and
then make several 2-3 shifts at the throttle position determined to be the most sensitive to
the 2-3 flare, This will allow the transmission adapts to tailor the shifts and may help to
eliminate the cold 2-3 flare. This condition is a NORMAL characteristic of the transmission, it
will not cause durability concerns and no repair attempts should be made.
 
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