c4 transmission rebuild HELP

The fact that you've got slipping in reverse and first at least will narrow the problem down. The C4 shares the "low band" for reverse and 1 on your selector. There's a reverse "band" that's tied into a hydraulic solenoid that will stop the outer band from turning and engage the inner ring causing the output shaft to spin in reverse. Sometimes if you've got to low of a fluid level there's not enough to push that servo all the way and lock into reverse but since you're not finding 1 nicely either I'll say its mostly one of two things. 1) you've got too much fluid. This can cause some slipping issues or 2) you put the valve body back together incorrectly.If you've got no transmission experience and its problem 2, check and double check that all your balls are seated in the correct spots. This is of course assuming that you didn't take apart all the valves and internals to the VB. Otherwise you might be best off either taking the VB to a professional or to buy another one. Seriously, Automatic transmissions are not fun to tangle with. It'll take you lots of spent time and $$ to get it right.

The simplest thing to make sure is that you've got all your clutch packs seated correctly, the servo's are free to move without stiction and that the little balls inside the VB are in their correct spots. Just by moving those from one spot to another can make a transmission work or not work.

To add to it if you're not finding "park" and the car is moving freely then you've got some other issues as well. If you can put the transmission in park by moving the lever on the transmission by hand, then you've most certainly got something wrong in your linkage. Otherwise you most definitely put something together wrong.