I don't really think that our timing belts can "slip". It's a "toothed" belt that rides on "toothed" gears so unless the belt is stripped or the tensioner has gone out I don't think you could slip a timing belt. Have you ever changed the fuel filter and fuel pressure regulators? My VX had a starting issue at Moab one year, and when I got back home I replaced my fuel filter (which was totally clogged because I couldn't blow through it) and my fuel pressure regulator and that seemed to fix everything. Both of those parts are cheap and, relatively, easy to get to so maybe give them a try first.
When you turn your key on the ignition to run (I think that's what it is), before you turn it once more to start the engine, you should be able to hear your fuel pump in the gas tank turn on to prime the engine, so that's an easy one to diagnose and make sure that it's working.
Those are my guesses.
"The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong, it usually turns out to be impossible to get at or repair."
-Douglas Adams, Mostly Harmless