I have a 4x4 S-10 truck. I live 5 miles from town it will go to town just fine, but coming back my truck starts to hesitate and surge around in any gear until I pull over and turn it off or it dies first. When I let it set for a couple of minutes it will go for a couple of mile then hesitate and surge again. I rebuilt the carb on it 4 months ago and was doing good till now. could it be the carb or part of the emission control valves