99 Suburban Won't Start After Parked Downhill

My 99 broke down on Christmas Day 100 miles from home. Fuel pump. Had it towed to the local Chevy dealer (after sitting in the cold with my entire family for 5 hours). The dealer replaced the fuel pump and after $650 and a week, we were on our way. Now, sometimes, especially when we've parked facing downhill (which is not a majority of the time) the truck will not start. I can hear the pump whinning in the tank but am concerned that the fuel pressure may be low. Anyone had problems like this? The truck runs like crap if we can ever get it to crank after one of these episodes. If we don't have any trouble with it starting, it runs strong. Any help or ideas would be appreciated. It's at the dealer again now. I'm getting really tired of this.

After looking at several other posts it looks like this will probably be fuel pump related (i.e. low pressure), and possibly caused by a poor electical connection (i.e. pigtail). I paid a GM dealer to replace the bad pump in December of 2004. If it is a fuel pump pigtail, should not a warranty cover this?

Thanks for your thoughts.

Parking down hill would have nothing to do with the pigtail wiring ,How much gas is in the tank when this happens? about 1/4 of a tank?? Suburbans have 42 gal tanks and that is very big and if you are low on fuel and park facing down hill you uncover the fuel pump because the gas that is still in the tank is now all at the front of the tank and the fuel pump has nothing to send to the engine. Also that is a sure way to kill the fuel pump fast because not only does the pump sent fuel to the engine it uses the fuel to cool and lube the pump

Just had a similar problem on my 97 GMC, dealer told me to start
looking for a gas stationn when you get just below 1/4 tank. Fireplug
is right about the gas lubricating/cooling the fuel pump. Also highly
advise to change fuel filter every 15/20K miles so your fuel pump
won't have any flow problems. We know now...