Thank you for the replies. I have done quite a bit of checking to try to determine what is going on. I know it is not a fuel problem, at least in the sense of FP relay or fuel pumps running. I changed the temp sensor 6 months ago when I had the head off for an unrelated issue and will check, but don't think that's it. It is just strange to me that this only happens when the engine is really warm, like after a nice long drive, but then starts up fine after even 5 minutes ? It doesn't even cool down much, and would continue to run fine if I hadn't have shut the engine off. I was really sure it was some kind of vapor lock problem, but as I said earlier, that doesn't seem to be it.