Hi, I jut got through rebuilding a C4 transmission for my 1967 Mustang. It has a 6 cyl. engine. I used one of those how-to DVDs, step by step, put it all together, and it won't shift. I can manually shift 1st, 2nd, but when I put it in drive it won't shift out of first. When I have it in second it drives in second, doesn't start from 1st at the stop signs etc. I replaced the modulator, still nothing. I don't think there's a problem with the vacuum line, I have it connected to the intake manifold, is that right? I took the thing apart, did the air test thingie that the DVD said, to shoot 100lbs air in whatever holes to see if the gears engage, and 1st worked, 2nd worked, and 3rd worked with a lot of pressure. Checked the valve body, saw nothing, put it back together, STILL NOTHING!! Can somebody help me? Is there hope for me? Should I sell the car? Should I nuke it?