I have an 87 IROC-Z and have had the car for almost five years. The problem I am having is not being able to manually throw the car into first so that it holds the gear. The only way the car goes into first is if I really get on it from a stop. I can go from 3rd to second fine and it hold second so I am not sure what the problem is. I even had the tranny rebuilt less than a year ago and thought that they might fix it but forgot to mention it to them b/c I was so mad that I tore it up in the first place. Any help is appreciated hopefully it is an easy linkage problem or something.

im not an expert but i think your shifter cable is out of adjustment now ud think that if a tranny place rebuilt ur tranny theyd adjust ur cable properly but if ur cable is in the right adjustment ur cable may be stretched, this may be why u cant reach 1st gear
so
1 cable out of adjustment
2 stretched cable or cable mount

Just more info I can physically pull the shifter into first the transmission just wont shift into first when I do. It will shift out of first and just hold second.

Stock 700R4's will not hold 1st gear to a high rpm. They will come out of 1st and go to 2nd on its own. With the TransGo Performance Shift kit it will hold 1st gear to any rpm. And you can find 1st gear at any speed. This sounds like what you want here.