Transmission question

[Vanguy16]

Transmission or engine or computer?

2010 GMC 4.8L SL.
56,000 kms.

Recently rebuilt transmission, torque convertor came loose so the shop said they rebuilt the transmission.

So, warm or not, if i lightly press the gas pedal and the rpm's rise above 1300 or so.. if I take my foot off the gas, it goes down to 1300 for about two to three seconds until it drops down to idle..below 1000.
This normal behaviour for these trucks?

Also, during low rpms, of you let off the gas so to take a corner, then give it gas again, the transmission kind of clunks into the next higher gear, usually seems between lower gears. Like theres "play" or "slip" in the transmission.

[CamGTP]

The idle rpm drop is pretty normal. The truck has a drive by wire throttle body so the throttle blade is the idle air control valve. If it were to just slam closed, it would stall the truck. The slow ramp down in rpm prevent the stall and make it a smoother transition from higher rpm back to idle. How much you notice it and how long it takes to drop back to idle may differ slightly from truck to truck but I wouldn't be worried about that.

 

Having not driven your truck to feel what the clunk feels like, it's tough to get a complete grasp of it. Though I will say that the computers do try to reach the best gear possible for certain speeds or emissions reasons. When you're coasting the transmission is kind of slipping as the torque converter does unlock on decel and will re-lock depending on gear/load so the jolt may be more noticeable.

 

It's been a while since I've driven a 4L60e in that body style to see if one drove similar to that. I'm so used to the way my 6 speed shifts that I don't really notice that type of issue.

[sefiroxx]

Had the same clunk on a rebuilt. Builder had installed an upgraded valve body that works better under higher load like faster acceleration.

Typically, they install an upgraded 1-2 accumulator setup that stiffness the shift. You might have to
, go back to original setup
. Tune the computer to change the shift point
. Modify the setup. You'll need to drop the 1-2 accumulator to see what was installed and what other have done (change springs, modify piston etch
' change pressure (which would change other shift points)