Ok, I put an 02 model 5.3 in my 1996 C1500, we kept the 1996 4l60e. I used a nelson harness and computer. Trans shifted fine behind old motor and computer, but now with the 5.3 and nelson computer, its having problems.

-when first started up, truck starts in 1st and shift normal up till 3rd, then it is pretty much stuck in 3rd, will not down shift when slowing down or stopping or go into overdrive when crusing. after a few minutes, the truck will skip and buck a few times (like its being shut off) and then the trans goes to neutral (no forward or reverse gears) untill you shut it off for 10 seconds and start it back up, then it starts over again.

-has a code for 3-2 shift solenoid
-when scanned, all gear solenoids can be commanded, pressure is at 90% all the time and computer always thinks trans is in D4.

Im lost, Nelson says the tunes for the early 4l60's and the newer are the same. they asked me to post on here and see what I find. Thanks