fuel injectors. if you havent got a tsb from the dealer. the injectors should be under warenty. gm now makes an updated model for the 5.7. the same thing happend to my 97 k1500. it would miss like crazy at high speeds or load. ping like hell too. but if you let this go too long the cats will suffer cost me 1500 just for the repacement cats. that sucked! good luck..
