I just got a 98 Dodge 4x4 extended cab with 5.9 cummings if you park it facing downhill it starts and runs fine, if you shut it off on level ground for more than a few minutes it will not start. Lift pump changed and seems ok. Can't find any leaks and check valve holds. No problem with power while driving. My first diesel but it runs great other than the starting. Any suggestions?

 

Have you checked fuel pressure out of the lift pump?

 

Mine was leaking at the T fitting where the over flow line meets at the back of the head on the drivers side. I don't know if the 98 has the same set up. I tried snugging up the fittings which works sometimes and ended up replacing the bushing. They are about $4 each. (edit: $8 each - 4 is too cheap. They are simply a short length of the proper size hose.) You need 3 of them but don't need the T itself. Cummins had a hard time finding them & had to go look at an engine. They are easy to get to with the stock lift pump moved out of the way.

 

Rotten return fuel line, it is allowing air into the system. Check all your rubber hoses at BOTH ends and replace with quality diesel rated line only.