I have a 1985 Monte Carlo 4.3 V6 its a trottle body engine. I have changed out the spark plugs and wires, i have also changed out the top raidiator hose, as well as the theromastat. It runs fine on the back roads, but when i get on the interstate when i get between 60-70 mph it starts running hot and missfireing. I have taken it to every mechanic around and none of them can tell me whats wrong with it. I've even have my car red lineing, so if someone knows whats going on or has had it happen to them please help me out!

 

Heyy! Welcome to the forum! Hopefully someone can help ya out

 

Welcome to the forum