Do you have a fuel pressure gauge? Could be an issue with the return line and losing fuel pressure, maybe the check valve that's in the return banjo on the vp44. It could also be the o-rings in the tubes that go to the injectors... to me it sounds like a fuel pressure problem and loses pressure when it sits.

68 Road Runner, 69 Belvedere, 71 Challenger Vert
340 barracuda, 01 Ram CTD, 95 Ram, 04 Ram, 85 Daytona turbo Z
66 GTO, 06 Magnum RT AWD. 07 Ram CTD, 07 Ram