The problem started about a month ago, the truck runs fine for an hour or so then all of a sudden it will start bucking and missing like crazy. I can decelerate and the problem lessens until I accelerate again. The idle speed is fine. I have changed the fuel filter, plugs, distributor, coil and timing belt, I still have the problem. When I changed the timing belt I made sure all the marks lined up on the different gears, re-installed the distributor and started the truck. I wanted to set the timing and cannot set it to specification (7 BTC), the closest I can get is 3 ATC. The truck runs but I don't have a lot of confidence in taking it out for a 50 mile test drive. Has anyone come across a problem similiar to this??

i had this problem once drove me crazy what it was is the po had changed the timing belt and when he put the crank bolt in he did not tighten it to spec and the crank gear walked back and forth the crank was fine but the key ate the crank gear and when you would start the truck it would idle fine but when you drove it for a mile or so it would run like crap and if you shut it off it would not start and when you turned the crank to line up timing marks it would be fine but if you put a timing light on it you could not do it and if you shut it off it would not start and when you turned the crank all would be fine and it would start so check the lower timing belt gear