I have a rebuilt transmission that's 4 months old, new silonoids on the tranny case(theres two of them), it's not shifting smoothly, tranny fluid levels fine, and the D4 light wont come on when i engage that gear but the D3, 2, & 1 will light up. it's almost as if there's no difference in D3 or D4. Don't know why it's not acting right.... is there something that would regulate when the gears shift according to the RPMs? If i let off the gas, itll change gears but will rev higher before switching if i don't let off the gas... im at a loss. Some ideas, anybody??

 

Pull your cluster and switch one of the lamps from D3, D2, or D1 into the D4 spot. Then jumper your two wire blue diagnostic connector. This will blink any codes that may be present in the TCU.
How is the down shift cable on the throttle body?
You want the slack taken out but you do not want any preload or pulling on the lever down on the transmission. Same goes for the throttle cable, take the slack out, but don't cause it to pull anything open.

If you have a volt meter, back probe the TPS and look for the signal wire. You want to see a steady linear change in the voltage from the TPS. If the TPS is not registering, the TCU will not command an upshift.

Another trick is to see how it shifts under WOT. Find a nice long empty onramp and floor it. Does the trans upshift? If so, I would suspect an issue with the TPS.