The next time you have a hard hot restart, do the plug swap. If that gets it going you have a fuel system problem, probably related to rest pressure. If it doesn't start you may have an ignition system problem. In that case check for spark. The impulse coils are known to fail temperature sensitive but not quite this way. Just because you changed some parts can't rule out that you may have done the swap improperly or the part you put in is faulty. The best test for rest pressure is to observe the rest pressure with a fuel gauge. Very easy to damage the "O" rings on the PPR when putting it back together. Once damaged you won't hold rest pressure long enough. The way to test that is to use the pressure gauge and block off the return line to the fuel tank. That way even if the PPR leaks you won't lose pressure. That will confirm if the PPR leaks. Bottom line, if the plug swap gets you going you will need to get a pressure gauge and do some troubleshooting.