I need help badly, my car stays in first gear until 28 mph,2nd goes until 35 mph,3rd goes until 38,and 4th kicks in at 57ish.
This is driving me crazy,i recently rebuilt the motor,pulled it out.So im thinking i knocked the TV cable out of alignment. Thanks Michael,

 

To adjust the TV Cable skip the book method and do this: Press the 'D' shaped lock button on the adjuster and loosen the cable setting (The black housing that the metal cable is in will move forward). Now, have someone floor the gas pedal while you check to see if the throttle plate is open all the way. Usually they are off a little and will wiggle. Do whatever you have to do to get it open solid. Now, with the pedal still floored, press the 'D' button and pull the cable casing (the black tube) back as hard as you can (putting maximum tension on the metal cable) and release the button. You now have the engine, tranny and gas pedal all in sync at WOT. Mark the cable casing so if for some reason it gets moved you can know where to put it again. The problem with the 'self adjust method' is that it bends things and puts them permanently out of whack. It is also the full TV setting, which is theoretically what the GM method does.

Bear in mind that you may have other problems but this is the first step. If you still have the problem you could have a sticky throttle valve problem which is quite common.