1990 Other Oldsmobile Models Help needed with my olds please

I have a 1990 old calais with a 2.5 4 banger in it, it's my winter bomb for the last 2 winters. I went friday and had the emissions test done to re new the plates. The guy doing the test said the car passed better then most newer cars. Anyways I left there and drove 3-4 miles and then it started missing and acting strange. I thought maybe there was some water in the fuel freezing it up so I poured in a container of gas line antifreeze and added 10 bucks worth of high grade gas. I babied it home. when it's in parked you can mash the gas to the floor with no problems but when you put it in gear and put a load on it it starts missing and back firing thru the top of the engine. I thought maybe a plug or wire went for a crap so I put new plugs and wires on the car and the same thing. What could be wrong??