I have a 1992 RV based on a ford E350 chassis with an EFI 460. Whenever I have a long upgrade(which is pretty darn unavoidable here in Colorado :^) the RV appears to vapor lock. It progressively looses power and sputters until it dies completely. This often happens immediately after the uphill when coasting down the other side. If I let it cool off completely it then starts up and runs like nothing has happened! The temp gauge never goes near the "red" on the uphill. This problem seems to be getting progressively more frequent although that might be just the summer temps.
The RV's engine and chassis is bone stock and only has about 45K mi. on it.
My best guess is the in-tank fuel pump but I'd just as soon not try shotgunning the problem. I know I have heard of others with similar problems but I've never heard the solution! Any experience or suggestions would be GREATLY appreciated.
I had a VERY similar situation with a 1989 Full size Bronco. Mine was totally temperature related. Let it cool w/ the hood open and it'd start right up. It was under warrantee, and was towed to the dealer. They replaced the fuel filter (!) and that fixed it!!! (I felt a little bit stupid as I could have taken care of it). Try that.. it's an easy job.
Another thing you may want to do is get a fuel pressure test gauge that connects to the EFI rail's Schrader valve. Soon as it dies, hook it up and turn the key on... see if you've got the correct fuel pressure. Your fuel pres. regulator or pump relay may be trying to die. Also, I wonder if the 'in tank' pump's pick up screen could be getting fouled with some junk in the tank, or possibly the pump's pick-up is loose.
One other thing... check the NHTSB's Technical Service Bulletin list... there may be a TSB out on your chassis. (www.nhtsa.dot.gov)
Go to rvamerica.com. This problem has been discussed many time. The fuel pump may very well be the problem but the current thought on the mentioned bb is that heat build up is the problem. One of the long time members of that bb has insulated his tank, lines, and installed a cooler in the return line. Has not had a real test of his modifications yet. As someone mentioned, change the filter first. Good luck,