Qmann

Don't know if anyone can help with this. I have a 1992 Blazer S-10 with the 4.3 Vortec engine which I completely rebuilt. It's the 4 door Tahoe version, automatic Transmission. During the rebuild, I had to over size the pistons and related engine components. I broke the engine in correctly and it seems to work fine until I need to tow my boat (3,000 Lbs). It loses power while towing. On the highway, just going up a moderate hill the speed steadily decreases until I have to press the gas all the way down just to maintain 45 MPH. Of course, the engine temp climbs very high.
The engine techs dealer and non dealer say everything is working fine when it's not towing and can't diagnose it. Timing is good and has been checked three times. I do notice a miss at idle and while driving there's a very light surge or jurkiness like a cylinder is momentarily pushing more than the others. I just know something is amiss and can't isolate the cause.
Does anyone have an idea what the problem could be? The trans was also rebuilt and isn't slipping (automatic). Do I have to update the computer chip or something? It has a throttle body and the injectors seem to be working well. Fuel pump pressure is good with a new filter. Timing is fine. The dealer and mechanics here are at a loss as to the problem. I already tried this problem in the S-10 forum with no response so maybe it more general engine stuff I should query. Any help is appreciated.

Richard Till

Any codes? 4.3`s aren`t a powerhouse and you`re pulling about as much as the truck weighs. Check ur plugs and wires. You`ve about eliminated everything else.