Help!!! Transmission Problem!

I just put a new rear end axle in my 89 Iroz Z28 and after its installed, I have no transmission but the only thing it works is when I start the first gears, and so on.. the parking and reverse gears works fine, but what im saying is I have to start the first gear and then put in drive, why do I have to start in first gear to combine it? 1st gear, 2nd gear, 3rd gear, drive, and overdrive, why first gear? is it my adjustment on my transmission is off or what? please help