89 GT auto shifts like crap!

My brother just bought an 89 gt with automatic. He got ripped off on it and needed to get the transmission rebuilt immediatly due to the overdrive being toasted and the car being extremely slow when acceleraing. It felt like the car was starting in second gear. So we had it rebuilt with the basic stock trans and it has overdrive now but it still feels like it has no first gear......it does it just feels terribly slow. Also the torque converter locks up right away and when you stand on it, it doesn't down shift at all really. It will shift best, which is still not good, when the sifter is in "D" and when it's in "1-2" it will not go into first at all. I dunno what it is so my question is, does the computer on these cars control any points of the transmission at all? The car was like this before and after the trans rebuild so i dont know what it could be. Thanks for any help in advance.

With the 1-2 issue, im talkin dead stopped, it will not go into first gear. it only shift good in D. I messed with the TV cable a little bit but it didn't really help, it needs to somehow get it to kickdown. Does the computer control the torque converter lock up at all?

Are you sure? I thought all cars since the 80's had lock up's? It revs up to like 2000 ish i think and wont burnout either. I know the motor is down on power but the transmission wont kickdown or shift right so that is what i want to fix first, again any other ideas are greatly appreciat.ed