Q&A

give it a shot of ether and see if it goes.
Im not sure about this motor but it could have a broken timeing belt.

Squirting carburetor cleaner into any hose into the intake manifold, reattaching the hose and going into the car should cause the engine to attempt to fire if the problem is a lack of fuel, the fuel you sprayed into the manifold will remain volatile for 10 or 20 seconds easily while you get back into the car to start it. Check to see if you have spark at the spark plugs. If you have spark, and fuel pressure at the fuel rail on cranking can you hear the fuel injectors clicking (try putting a screw driver metal tip against the body of the fuel injector ,put the handle end up to your ear and get a friend to crank over the engine you should hear a clicking sound. You are in effect using the screw driver as a stethoscope.

May be a long shot but had the same problem with my 5.7. distributor module!!

I would try the distributor module to . if that does not work do the minor checks first . if you have poured gas in throttle body and it has good firing power ; then check your catalytic converter. since you have almost 300 thousand miles its worth a shot. if that converter gets stopped up your car can not breath in and out . go under your truck and knock the heck out of the converter with a hammer.