Just bought a 2000 silverado regular cab.
it has the 5.3 with some light mods 100k miles
also a 800 hp buillt tranny, with a 2500 stall in it, by a very reputable tranny shop.
i bought it from a buddy that had hopes for it, but had too many things to build so he wanted to sell it. the tranny was just built and dropped in with zero tests, then i bought it.
Now for the problem:
it wont shift out of third, unless i manual shift it to second. so ive been doing some research and if the solenoids arnt receiving 12v then it goes into limp mode. That is all i know, i am big with electronics, just not mechanical internals (engine,tranny, rearend). is this something i possibly can fix? does the new tranny need to be tuned? thanks for your help!

it has 3 codes:
P740- torque converter clutch malfunction
P785- Shift timing solenoid A malfunction
P1860- Tcc Pwn Solenoid circut elelectrical malfunction,

 

talk to the shop that rebuilt the trans, take it the trans wasnt recently rebuilt or it should have a warranty

 

Looking more, this year had bad ignition problems. A few people have said that if all three codes pop at one time it's a bad ignition switch. So I looked a little further, the ignition switch is alot newer. So im stuck again.

 

I'd check for damaged wires. Also verify everything is installed correctly in the valve body. One part installed backwards can cause problems like you are seeing.

 

everything was good after a tune. guess it needed more pump pressure with the higher quality parts in the tranny.