Ok, I have a 351w with a C4. I bought the C4 from a local guy who was selling it for a friends widow. He said he wasn't sure what was done (or not done) to the trans. It's a 74 C4. I pulled the pan when I bought it, and it looks like it was rebiult. everything in it looks new. I bought a brand new factory stall converter, filled it with a couple of quarts if fluid and installed it. I started the truck without putting any more fluid in but only for maybe 30 seconds. Today, I filled it with fluid and put it in reverse. It started to move backwards then stoppped. Now it won't go into any gear or go anywhere. The vacuum modulator wasn't hooked up. Would it not go in gear because of the vacuum??? Did I fry the pump by running it without enough fluid??? Does anybody have any suggestions???