Engine misses at acceleration on 95 E350

I have a 95 e350 14' box van and after about an hour the engine(5.8) starts to miss fire when accelerator is pushed. I am thinking now that maybe a vapor lock situation, but I do not know. If I stop and let it sit for about 5 min, it will run fine after that. It will run fine at idle, but not accelerating. I have run fuel system cleaner, changed fuel filter, changed coil and plugs. I was wondering if anyone else has had this problem. The engine does have 194k on it.