help need .my car runs fine but in 3 and 4 gear at 2000 to3000 rpm the car back fires and the rev counter jumps alittle this happens every time, past 3000 revs and the car runs fine.i have tried a dissy off another car and it did the same thing,also checked the timing and this is spot on,and check plug gap and they are ok.please help because i am running out of options