chevydog66

iTrader: (1)

72 GMC 1500 truck with a junkyard stock 01 6.0ls and purchased new 4L65 trans 4 years ago only 10k miles at the most. Just swapped rearend gears from a 3.07 to a 3.73. First test drive after it has sat all winter and now trans is slipping like crazy in 1st and 2nd only above 2800 rpm. It's not in limp mode. No check engine light. Speartech did the computer and harness specific for the truck. Speartech says should be no problems with computer. And trans fluid is reading way too full on dipstick. Trans is slipping bad, almost like throwing it in neutral above 2800 rpm. Should I just pull trans??

ls1nova71

iTrader: (4)

Did you change the tune to the new gears? Are you sure it's actually slipping and not just not shifting at the correct time due to the wrong gear info in the tune?

chevydog66

iTrader: (1)

Haven't changed the tune yet. This was first test drive after gear swap.

Old Geezer

iTrader: (3)

" And trans fluid is reading way too full on dipstick."
Correct stick?
If so, get the fluid level corrected, then go on to more t/s.

ls1nova71

iTrader: (4)

How far have you driven it? Maybe the torque converter is leaking down? Don't know how else the fluid level would have risen if it was right before.