Two-fold question - This question has two parts: 1. Under what circumstances does the torque converter normally lock up in the 4L80E? 2. I took a little road trip today ...

This question has two parts:

1. Under what circumstances does the torque converter normally lock up in the 4L80E?

2. I took a little road trip today (about 75 miles), and noticed something funny happening to my transmission. On the way back, the torque converter didn't lock up until after about 20 minutes of cruising at 60 MPH on the freeway. After this, it stayed locked until I took the cruise off; when I put the cruise back on, it would only lock up again after the transmission temp touched 150. When the converter was locked, the temps would dip to about 125-135 (outside temps were about 45*F). Engine temp was normal; I was at 60 for nearly the entire trip, both ways. MPG numbers were great; they were just a little higher when the converter would lock. However, the RPM would go up 200-300 if it was unlocked.
On the way up, it didn't lock until we had been on the road for about 15 minutes, but this was from a cold start, at 25*F. Even more strange, also on the way down, I had to pass some cars, so I popped up to 65-70 MPH, with the converter unlocked. I stayed there for about a minute, with the RPM holding at 2500. Then the check engine light started flashing, and I dropped back down to 60 MPH. The light stopped flashing shortly thereafter. When I hit traffic, and had to stop using cruise control, it would lock up right away. What gives? Is this somehow normal operation? The only modifications I've done to the transmission are flushing it completely and filling it with AMSOIL Fuel Efficient synthetic ATF, and it's also got the Hypertech programmer, which does change the way the transmission behaves (but not too drastically). It's got the stock 4.10 axle ratio, and stock tire size. I'm pretty sure it has done this since I purchased it, but since I'm becoming more and more an anal truck owner, I'm starting to notice this things. Any ideas are helpful...

I would suggest seeing if you have any codes in the system. You could have a solenoid malfunctioning. Hard to really say what the problem is. Try starting with getting the system checked for codes.

I haven't experienced any other issues... driving around town, it works great.

Checked today for any codes. Scanner showed 0 codes.

Hard to say. It may be a mechanical type problem within the transmission (like a seal leaking or a worn clutch pack).

my 2008 silverado 4.8L V8 wont shift into 2nd......what causes that to happen...

Thanks for the input, Jordan. I did a lot of freeway time again tonight, and didn't have a single issue. I don't know why it has acted up twice on that single stretch of road, but I'll try not to worry about it.

jack101789 wrote:my 2008 silverado 4.8L V8 wont shit into 2nd......what causes that to happen...

It could be a lot of things. Anything from a bad solenoid to a worn out clutch pack.

Update:

I drove the truck on the freeway with the programmer off. Sure enough, the moment I hit cruise going 65 MPH, the converter locked up right away. I hope Hypertech will have some answers !

I didn't know you had a tuner. It does sound like it may be a tuner setting issue.