2005 Silverado Hard 1-2 shift when warmed up

[The_Hamster]

2005 5.3 1500 4X4 Auto

 

1-2 Shift when cold is smooth, no issues. Once warmed up though it holds first too long and bangs into second a bit hard. 2-3 and 3-4 are smooth.

 

Transmissing is a "gm factory rebuild" according to the sticker on it, out of an Avalanche. My original transmission crapped out 2 years ago. This one came out of an Avalanche with 75k miles on it, but also has a factory rebuild sticker on it but unknown when that was done.

 

Fluid is fresh from the install of the transmission about 10,000 mlies ago, DEX 6 from the dealer.

 

Any solid ideas on this issue? No check engine light illuminated.

[txab]

If dealer installed, I'd let them look at it and make programming adjustments. Line pressure may be a bit high.

[The_Hamster]

Not dealer installed. Got trans at a wrecker and put it in on my driveway.