My 1999 gmc sonoma s10 upon startup sputters and stalls unless i give it gas right away. It will run, but after slight acceleration, it sputters and will continue until i let up. It sat with old gas for a full year and through all seasonal conditions. Ive put a new fuel filter in and dowsed my tank in injector cleaner thinking sediment buildup at the bottom of the tank could be the problem. I need help please.