Sounds like it's probably losing fuel pressure sitting on the incline. It's probably not the pressure regulator, but the anti-drainback valve built into the fuel pump, which is usually the first part of it to fail, especially on aftermarket pumps.
Since that valve typically fails long before the mechanical parts of the pump, the simple live with it solution is when you start the Jeep, turn the key to the on position for 2-3 seconds to allow the pump to prime the fuel pressure, then turn the key over to start. Should fire right up.
2003 WJ in Jeep Green Metallic
, 4.0/242/4.10's. 4" Teraflex springs w/ RE monotube shocks and IRO short arms, cheap intake w/ amsoil filter, 2.5" hi flow cat and back exhaust, lots of lights and other misc crap.
Check out my build thread here: Life lessons and budget build