i have a 02-03 sierra and it wont start.. it cranks over then suddnly stops cranking like the batteries dead. then starts cranking again. while it is cranking it wont fire. i believe it fired once and then back fired but im not sure.its dark out so cant see very well but i checked every possible connection i could find plug wires everything my i could see and/or feel. also as i was driving earlier today down the highway it "chugged" kinda like it may have miss fired but then after that it was fine for quite a while then did the same a while later and that was the end of problems till i tried to start it.