I have been working with my sisters 2001 2500HD for a while now keeping it going.

If it is parked at an angle where the front is higher than the rear the truck will NOT start, No if and or but about it. Have to prime the system to get it to fire.
The sucker gets 25mpg average driving and about 20 if you are laying some rubber down at every other stop light.
When it is idling the rpm surges up about 50RPM and drops back down instantly and it does this about twice a minute.

I was wondering if some of this was normal.

The truck is bone dry, it is not leaking a single drop of anything (well, except the axle seal is going).
So far I have changed all the u-joints, wired in some new speakers, changed the oil about a dozen times, and done the water pump (something I swear I'll never do again).

 

fuel filter?

 

check the fuel filter first, replace it even if it has 5k miles on it. and check for leaks in the fuel system.

 

the no start on a hill is most likely the fuel filter housing. its an internal issue with that adapter that loses prime.
the idle surge is most likely going to be the fuel pressure regulator (FPR). if you want to see it graphed take it to a dealer and have them plot the rpm, actual & desired fuel pressure, when it surges you'll see a jagged line...

 

^^^^^^

 

i would put in a new fuel filter and see if that will fix it.