I have a 2000 silverado 1500 with a 5.3. Got it 2 years ago and changed the plugs, wires, and threw a k&n filter into it. A couple weeks ago I was driving home on the interstate and my truck started to choke and sputter. When I hit the gas it would get worse and felt like it was backfiring. After pulling over for 5 mins. I got back on and was fine for about 20 miles till it did it again. Whenever put the gas to the floor it would downshift hard and excellerate to 75 then cruise for awhile and slowly lose power down to about 40mph. When I got it home I checked my wires, cleaned the air intake, and oiled the filter. After I put the filter in it got worse to the point were one day I could limp it to work and the next time it would barely idle in the morning before it died.I replaced one of the front O2 sensors. nothing. I cleaned the maf sensor and replaced the fuel filter and it got better to were I could get round town most the time with the occasional hiccup and backfiring incident( i think oil from the filter clogged the maf???). but on the interstate it will run decent enough to get me around but occasionally it either stumbles and backfires when i stomp on it or it will downshift hard and excellerate hard up to the speed i want. I have scoured the forums looking for answer and think either i need to get new plugs( wires seem fine), new maf, or maybe the fuel pressure regulator. I plan to get the fuel pressure checked tomorrow and have codes on here too. cel has been on and off since first occurance. really hope its not the fuel pump. Any advice would be appreciated.