HELP!!!!!!!! Sonoma falling flat on face after driving for a few min

Ok Im new to this forumn, I just bought a 1993 gmc sonoma with a 4.3 w vortec. I got misled into thinking this was a good vehicle cause after 24 miles. While driving the truck would not accelerate and start spitting and sputtering and backfiring. Id let off the gas and it would idle fine. So I turned off the truck turned it back on and it was fine but a lil farther down the road it repeated the problem. IVe got some ideas to what it might be, but I need others advice the more the better. Please help me out! I think i got jipped out of 800 bucks!

Welcome to AF.Check fuel pressure at the rail for starters. Look for at least 60 psi.