I have an 88 with a newer crate engine with 12,000 miles on it. The transmission was also rebuilt 5,000 miles ago. This was put in when I bought the truck last spring to take my little guys fishing and camping. Recently the pickup started sputtering and backfiring when I step on the gas while it is in drive. It idles fine and the sputtering and backfiring only seems to happen once in a while. It is either after it is warmed up and driven several miles or after it is started back up after having driven it. If you shut it off and start it again, it stops. When the engine was replaced, a new distributer, plugs wires, knock sensor, and o2 sensors were put in. I just changed the fuel filter when this started and it did not stop this behavior. I cleaned the EGR valve thinking it might be sticking, again, no change. I checked all the plugs and they look great, I also am not getting any codes.
I read it might be a MAP sensor, I have one on its way but wondered if I might be on the wrong path. I don't want to throw a lot of money into changing parts that might not be bad. I have always had good luck finding advice and I am very appreciative if anyone has any input. Thanks!