I have a 1991 Chevy S-10, 4.3 liter. I have been dealing with problems on the truck since I purchased it a few years back with about 200,000 miles on it. I had the engine rebuilt, bore 30 over, by a reputable machine shop in my area about 8,000 miles ago. About a 1,000 miles after that had the transmission rebuilt with a stage 2 shift kit. I put single muffler dual outlet flowmasters on it as well as a aftermarket holley throttle body. I have had problems with the truck running hot. When it gets warmed up it runs between 220-230 degrees. I have replaced the thermostat, water pump, radiator, and clutch fan. Replaced the distributor cap, rotor, egr, plugs, wires, etc. Etc. Not to long ago the vehicle stumbled somewhat, if you were driving down the road and let of the gas for about 30 seconds or longer and then got back on the gas it would take a few seconds to get anything in the pedal. That problem has seemed to disappear. The more I retard the timing the better the truck runs. If I set the timing to spec. 0 degrees it runs sluggish. No matter where I set the timing my running hot issue remains. I ran a cheap gauge straight from the block to eliminate the possiility of error in my dash gauge. It may also be a help to know that within 200 miles of putting the rebuilt engine back in the first time it threw a rod - then was rebuilt again. A few weeks ago I put the stock throttle body back on because the truck was still running kinda funny and I had gas in the oil. Since I have not had gas in the oil and it seems like its running like it should (i think due to the fact that I never had my intake ports bore to match the throttle body bores) - all but the hot issue. My only symptoms now are running at 220-230 degrees - but wont go higher or overheat and if it is at that temperature it is very hard to start. That was alot of random information but I think it will help give a little background on the truck. I am a mechanic myself and the problem baffles me. Thanks for an suggestions you can give.