OK so I drive my truck to work ran great all the way there parked in the parking lot idled for a few and shut it off. Came out at lunch went to start my truck and its missing so bad it will barely run and if you get it to run its seems to be maybe 3-4 cyls firing. The code I am getting is an p0300 my favorite lol anyways first thing came to mind was what the hell put a new ac cap and rotor on it so i did no change,new fuel filter, same fuel pressure is at 56 psi. timing on scan tool inset jumping around distributor is tight no play side to side. Drained fuel replaced with new same. Got running hooked vacuum gauge up and makes poor vacuum because its only firing on a few cyls but needle is steady. plugs are new so are wires all ac parts learned the hard way before. had ign module tested good. ohmed out coil within gm specs. I'm thinking maybe spider but not sure. any ideas??

 

Did you properly gap the plugs and did the weather change any from the time you went to work to the time you went to lunch. The reason I asked about the plugs was because the book that came with the truck said to gap the plugs at .040 and the parts place said to gap them at .060 and thats a big difference. Oh and the part store is the one you want to go by.

 

What does that mean? If the timing is 'jumping around', points to either the CKP or.. more likely.. the distributor pickup.