I have a 99 Durango and have been having problems with it hesitating when I accelerate slowly while at speeds of 30mph or more. If I keep the gas pedal in the same spot, it seems fine. When I push on it for a hard acceleration, it runs fine. But push on the pedal slightly, like when try to maintain your speed on an incline and you feel it jerking you around. I'm not getting any error codes. I have already replaced the oxygen sensor and the fuel injectors. Is this a spark plug issue? A vacuum issue, I don't hear any hissing under the hood. Just trying to find out if it's something I can fix before I take it in to the shop.