rough running chevy truck

[B radHuff]

i have a 1994 chevy truck 305 tbi upon acceleration truck starts to run rough it makes the exhaughst sound like it hase a leak but it does not . so far i have changed the following: plugs,cap ,rotor,bypassed fuel filter,removed and cleaned injecters,removed cat converter,brand new 3 inch exhaughst, have read codes several times only to get the 12 to come up meaning all good, i have thought of possible blown head gasket but it does not show any other signs of that does not get hot oil is very clean,the condition seemed to be on and off at the beginingbut is now getting a little worse,seems to do better in the morning for a little wile the only thing i can think it may be is the dist modul or the plug wires {new last summer}any ideas?

[ChevyTech007]

Sounds like it might be popping back through the throttle body. I would pull both valve covers and start it. Look for any rocker arm not moving as far as the others. Possible lobe worn off cam or bent push rod.