I have a 03 Durango with 19000 miles about a month ago it started hesitating and backfiring when cold. dealer first said it did not exist now says my valves had carbon on them. The dealer cleaned them but it is still having the same issue. the dealer says they have many of these and I think I am getting the run around with the valve decarbonizing at
19000 miles. is anyone else having the problem. no computer codes