My 2001 Suburban 2500 is having trouble starting. The problem first appeared when the fuel tank was low, and has now progressed to all the time.

Sounds like your fuel pump is going bad. They're not hard to change but they are expensive.

Put a fuel pressure gauge on it and check the cold start fuel pressure. Make sure it is up to specs.
How is the tune up end? Like plugs and fuel filter and exc.
MT-2500