I went for a cruise in my 72 Challenger last night and had some 727 tranny trouble. When I left home it felt like it wanted to stay in 2nd but eventually shifted and did fine. After cruising for for about 30 minutes it started feeling like it was slipping or more like going into neutral. I headed out from the cruise and on the way home it started getting worse it started going into neutral as I was driving when I let off the throttle it would engage again. It finally went into neutral and would not engage at all. I stopped in a parking lot figuring I would need towed home. After about 10 minutes I started the car again and the tranny worked fine for about 3 miles then it did it again. I let it sit for about 10 minutes and it worked again. When I got home it wouldn't make it up the slight incline my driveway has. I let it sit for about 10 minutes added some Mercon 5 fluid in it fired it up and was able to back it up and pull it up the driveway to put the car away. I couldn't see any signs of a leak at all. This tranny has about 1,000 street miles on it since a complete rebuild using billet everything and an ACC Boss HOG 3,500 rpm stall converter. Does anybody have any ideas of what could be wrong before I take it back to the guy that built it and get smoke blown up my *ss ?