Dieselmechanic

I have a 1977 Chevy Scottsdale C20 that has a problem that I have no idea what it is. It has just recently started to happen I will be cruising along on the freeway and my truck will start to lurch, jump, shimmy and shake like it's going to die but then it won't. I will have to find a happy medium on the gas peddle were it isn't adding to much or to little fuel and it will then drive fine. I need to figure this problem out as soon as possible before something major happens. Does anyone have any ...