what happens to your fuel pressure when it stops running?
Does it stay up at all? I wouldnt rule the fuel pump out just yet or a stuck
EGR. Did it
start this behavior after you changed the fuel filter?

You can rule the battery out if  its cranking strong each time.

my .02,  maybe even try reading the codes. Theres a zillion ideas.

Check and clean the IAC valve and it's passages. The valve pintle can
get gummed up with deposits and stick. May or may not be the problem,
but it's easy to check.

Pete C.

If yours has the 4.3 Vortex engine, (you should tell the engine size),
55 psi/running is right where it should be. 58/64 psi/not running. With
the problems that your having, it sounds like the fuel pressure
regulator is leaking, and/or one of the plastic feed lines on the
"Spider" injector is leaking. (these engines are noted for these
problems) Put your fuel gauge on, key on/engine off, let the pressure
build, then turn the key off and keep your eye on the gauge. The gauge
should drop 5/10 psi, then stop, and maintain that pressure for 10
minutes or so. If that's what you get, then it isn't a fuel
problem. Look for a vacuum leak, carbon/oil gunked throttle plate.
After you rule out all the basics, you'll have to hook up a
scanner/monitor and see what ain't doin what it's posta. If your
gauge doesn't maintain pressure, then the fuel system is "leaking
down" somewhere. (the needle on your gauge will drop, and keep
dropping, about as fast as a second hand on a clock) You don't want
to run the vehicle too much if you find it is the regulator and/or
"Spider" leaking. They are located inside the top half of the
Plenum. The gas that is leaking can/will drain through the threads of
the intake bolts and into the oil pan. Too much gas in the oil thins
the oil and hurts more stuff. If you have to change the regulator
and/or "Spider", it's a good practice to change the oil.