Hello to all! I have a problem I'm hoping to get some help with. My work truck is a 1976 Chev 1 ton dually, standard, with a PTO dump on it. Single tank, passenger side, hydra-boost brake booster. Originally came with a 350. I put a 454 in there. it came out of a 1979 Suburban 1/2 ton, with A/C (but I didn't re-install it) and it had a vacuum booster. Ever since late November it's been running perfectly. I have a 12 foot dump box on it, I've had 4000lbs in there no problem, no bogging, nothing weird, no loss of power going uphill. Then last week I noticed it bogging a bit going up a hill. Definitely felt fuel related, so I changed the pump and filter, still bogged under load or uphill. Got the carb professionally rebuilt, still no change. Did the dist. cap, rotor, coil (hei), plugs and wires.

Still bogs down like it's not getting fuel. Mostly going uphill, or within 10 minutes of highway driving (40-60mph)I have to pull over on the side of the road and wait a minute, then it runs fine for another 12 minutes or so. Only time it runs 100% is in town stop and go driving. When I changed the fuel pump I noticed that the the return line outlet was plugged off, ran fine without it until that point. I even tried driving with my filler cap off, no change. Any suggestions as to what to try next? Thanks in advance!

 

almost sound's like a fuel line is collapsed ,or the fuel sock on the tank pick up is plugged .

 

i suspect ignition coil and/or module. both will run fine for a bit, but when they get hot they may basically shut down if they are getting worn.