Engine Performance problem
1996 Chrysler Grand Voyager 6 cyl All Wheel Drive Automatic 131000 miles

when i drive the van, if i exceed 40 miles for a period it starts riding very rough and in unable to accelerate then it cuts off. if i restart it comes on but its shaky then it cuts off then after sitting for about 30/40 minutes, then it rides again. I've taken it to two mechanics and all they tell me its an engine misfire, why is that?

If it is running rough and cutting out, you must have a check engine light. Go to parts store (Autozone, Checkers, Kragen, O'Reilley, whatever you have in your area) and have the computer scanned. If two mechanic said engine misfire, the scanner will let us know which cylinder misfires. Get the codes for us.