Hadnt thought to check if carb opened all the way.. Checked and yes it does. Engine just runs ratty as you put load on it in 3rd. It sounds more like it is having a hard time revving rather than something causing a big load and keeping it from revving. Dont think it would rev out completely under normal 3gear load.. Flat paved street.

Rear gear is 5:14... Shouldnt take much energy to roll truck down flat road at 25-30 with no load

Im leaning more towards fuel issues


Old Truck addict
1950 chevy 1 ton napco
1956 gmc 1 ton dually napco
1954 chevy 3/4 ton napco
1957 gmc civil defense napco panel