1995 GMC Jimmy Stalling out

My truck has just had a fuel pump out on a couple months back and it was all swell and dandy and then starting out of nowhere, while driving to and from work my truck would rev itself up repeatedly. Recently, my truck has struggled to start and ehen it does- smoke would come out of my exhaust pipe in puffs of grayish smoke. It wasnt a constant smoke either, puffs every couple seconds. It started to stall out on me while accelerating and slowing down. I just put in a new idle air control sensor and hoped that would resolve it, but it didn't. What could it be? Does it need a tune-up or is the motor going out on me?