Clein1996

I recently rebuilt my C4 and installed it in my mustang. When I went to test it up on stands I had every gear. When I put it back down on the ground I had every gear except reverse. It seems to be in neutral when i try to put it in reverse. I checked the reverse band and the pins and they were in before I put it on the ground. The other thing I have noticed is that the idle gets very rough when I have it in gear with the brakes on. I suspect a vacuum leak and that the modulator may need adjusted but I have very limited experience. If anyone has any ideas or help that would be great. Thanks!