Chevy Mechanic
ASE certified.
While driving on highway and you let off of the gas the vehicle will keep acclerating. you have to hit the brakes to get it to slow down. We was told the carbarator needed over haul. We had to end of putting a new one on. They was also going to lube the speedometer because it was jumping around. We also had a tune up and rear brakes done. When we got the vehicle back it seem to run very good but the speedometer was not working at all. We found out they did not connect it back where it goes into the transmission. We then reconnected and test drove. It started doing the same thing where it acted like the acclerator would stick and you would have to brake hard to get it to stop. This is mainly highway driving. you do not notice it with city driving. There is no curise control on this vehicle. This is the speedometer not the tachometer.
If the speedometer is jumping around that usually means the cable has a kink in it or too many tight turns. Remove it from 1 end and let it unravel and put it back on.
Is the carb throttle just sticking open, if so spray the shaft down real good with some carb cleaner, also check the tension on the return spring, if not enough to snap the throttle back closed either move it to put more tension on it or get a stronger 1.
Ok now that I read everything you replaced the carb, then check that spring and get the kink out of the speedometer cable and you should be ok.