Gass is not going in to intake

If it cranks and cranks then finally starts and slowly picks up speed you may have a leaking fuel pressure regulator, unfortunately this truck has an injection system know as the "spider" and everything including the regulator is under the upper intake manifold so you can't see it leak. GM makes a kit that replaces the spider and poppet setup with real injectors and I think it comes with a regulator. Do this, find the injection test port left rear of the air intake remove the plastic cap then have someone turn the ignition switch on to prime the system then press the schraeder valve and notice how much gas sprays out, next prime the system again but this time wait 5 minutes then press the schraeder again and the spray should be the same if there's little or no fuel coming out replace the regulator and I advise changing the injection system over. I hope this helps. Take care.

Preasure your fuel tank. Take a cloth and put over your gas tank fill and use a air compressor to blow air into the tank to build presure. This should build up presure and react the fuel pump to pick up the fuel.

check for gas leak if none found these had a problem with the spider injection system inside the intake cracking causing a leak and no start due to the poppet injectors not opening due to weak fuel pressure. these operate at 56lbs pressure and its critical.

Yes very common problems with the "spider" fuel injection unit.
Remove the top of the intake manifold to access the FI "spider unit"
The injectors can be replaced separately. Also sometimes it's the pressure regulator that's bad, and leaking so check for that too.you can check the injector spray pattern if you are careful doing it.(disable the coil, have lots of rags and a friend crank the motor while you check the pattern of each injector) (hint - if you are really cheap you can actually "clean" the end of the injector with a small screwdriver , try to roll the ball around to remove varnish, then recheck the spray pattern.

The easiest way is to swap the intake manifolds.

Wow, that's interesting, I'm trying to think how you could be getting gas in the oil. I'm guessing the gas on top of the motor is coming from a leaking O-ring. You maybe have a nick or tear in one of the O-rings in that area. It might only leak at certain temperatures with things expanding and contracting. Try wiggling some of the lines and fuel pressure regulator to see if you can make the leak a little more obvious. As far as gas in the oil the only thing that I can think of is leaky injector and the gas running down past the piston rings. I guess it could leak down past the intake manifold into the lifter valley but, I find that hard to believe. Good luck with that one, have a Happy New Year!!!

You could possibly have to replace the spider injection assembly. Or the regulator unit to the spider injection rail.

This fuel pressure regulator is a component part of the SFI (sequential fuel injection) assembly, sometimes referred to as "spider". It resides inside of the air intake plenum and is accessed by removing the upper half of the intake. 
Good luck and hope this helps. 
Most of the time when your having problems, it's most likely going to be the whole spider unit. GM has been know to have problems with this type of fuel injection system. 
Check the vacum line to the fuel pressure regulator at the back of the spider housing by the high pressure fuel line. You can see it just in front of the distributor cap and spider assembly.

the injection relay,if memory serves me correct there is a bank of three under a cover on the offside front wing but i carnt remember which one it is but they are all the same

The vortec motor has been known for the so caller spider assembly which is the fuel injection set up inside the intake manifold going bad.The regulator starts leaking wich puts extra fuel into the motor.If that is it you should change the whole assembly.