We wrapped the fuel line on rm38a1 with heat tape and then also put some heat shielding around the exhaust manifold.... When they designed them that heat from the manifold keeps them running great in cold weather, but in the hot temperatures like you pointed out we've had the same issue. Once we wrapped it with some heat insulation and put some header wrap around the manifold the problems on hot idle or hot running were minimized. Brand new fuel pump so there was More than enough pressure.