I've had tbi on my k5 since dec. Its always ran great. But over the last month its started studdering and backfiring. I thought it was just a burnt plug wire but I changed them today and it didn't help it. It will crank and idle great. Put it in drive and it wants to die. Pull off and give it the gas and it studders and backfires to the point I can't go over 5mph. Could someone please give me some ideas of whats going on here. I think its a lean backfire, could it need a new fuel filter or is one of the tbi sensors gone bad?