Starting difficulties after sitting 12 hrs
 

I have a 99 RAM 2500 diesel 4X4 with a manual transmission. This truck has just over 250K.
The injector pump was replaced about 225K. The lift pump was originally replaced at about 120K and I just recently replaced it again in hopes to fix this problem. Also the fuel filter is new and made no difference or change. The truck starts and runs fine and gets good mileage normally, but......... After its been sitting 12 to 24 hours it has a starting problem. The truck will start immediately (if on a flat surface or downhill with the front of the truck lower than the back) run about 10 to 15 seconds then die from some obvious fuel starvation. It will take a good minute or 2 of cranking before it will start after that. All the fittings, fuel and injector lines and banjo bolts appear tight and no visual or obvious signs of leakage. If the truck is parked on my uphill driveway with the front of the truck higher than the rear, it just won't start at all until after the minute or 2 of cranking. Once started the truck works great all day.
I think its safe to say there is air working it's way in some way somewhere, but I don't know how to determine source. No obvious visible leaks. Any suggestions guy's?

Sorry I posted this in the wrong place. I'm new to site and still working my way around.