ok here's the problem 1991 e250 with a 4.9l .
different info from different places one said it CAN'T vapor lock the other said it can . what say all you smart folk out there if it's not that maybe the coil is
dyeing on me . the high 90s worse in the 100s after being on the road for going 3 hrs starts cutting out and finally quits let it set and cool for about 30min it will start and run for 1/2 hour then it starts again any ideas ???

 

Fuel injected vehicles are not "supposed" to develop vapor lock due to the higher pressure in the fuel system.
The coils on those years were very troublesome, however, and for the cost of a new coil , I would go for it.
Those sixes were quite reliable, but it would be a good idea to confirm if the problem is either fuel pressure lost or spark lost. Once you determine which it is ,we can go from there. If you check for a healthy spark when it quits , you will either have it or not, then we go from there.