I have a 2000 Tahoe z71. It runs fine and fuel pump appears to work fine. However, if it has been sitting for a while, it is difficult to crank and can kill the battery. It appears to not be receiving fuel until it has turned over a lot. Could this be related to fuel pump relay? Any suggestions.

If you are saying the engine won't start easily, replace the Ignition Control Module (ICM). These are very problematic components. I recommend replacing them every 120,000 miles or 10 years, whichever comes first. Simple 5 minute DIY job. Also, ensure the platinum spark plugs have been replaced in the last 50,000 miles. Only use the same ACDelco plugs that originally came in the truck.

Background on ICMs:

Conceptually, the ICM is a large output transistor (switch) controlling current through the primary coil. ICMs replace points and condenser in older vehicles. In the primary coil, current builds to 5 to 12 amps, generating lots of heat (due to inductance). Then, the ECM controls when the ICM "switches off" current to the primary coil, causing amperage to go to zero. When this happens, 12 to 14 volts in the primary coil is "stepped-up" to 30,000 volts in the secondary coil. This process creates a "type" of alternating current required for the coil (step-up transformer) to work. In a properly working ICM, timing is precisely when needed to fire each spark plug. Failing ICMs, however, don't always fire when they are supposed to.