1993 GMC C1500 • 125,000 miles

Ive been having issuses with my truck not running right and I was wondering if you could help me out. It startz up fine but once you let it sit for a while the engine starts to shake and cut out. When im driving I hit the gas and it doesnt resond like it should. When I roll up to a stop light the oil pressure gauge will drop all the way to 0 then then engine starts cutting out. My dad and I fixed the timing on it because it was off but that didnt fix whatevers wrong with it. We checked the EGR valve and that works. I cleaned the throttle body really good yesterday that didnt make a difference. And just the other day I replaced the fuel filter because that was congested. Once again that didnt fix the problem. Any help at this point would be greatly appriciated. Thanks
March 9, 2013.

Start with fuel pressure test. If it is a throttle body system it is 9-15 lbs. If it is a vortec, it is 60-65 lbs