Are you up to date with oil, oil filter, air filter, Basic tune-up stuff?? If it jerks when under a more severe load, but just has low power when under normal load, i would start by looking into your electrical system. Have your alternator checked(they have been known to cause vehicle to idle low, and respond jumpy) when they are starting to die. Also have your coils(little black box attached to every spark plug wire). If it is still driveable then try to check all you can before getting a mechanic to do it. Also does the situation get worse when it is wet outside? have you drove the truck through deep water?