My Dodge Dakota is running fine but if I slow down to a crawl, the motor chugs and if you step on the gas, it backfires and hesitates before accelerating. The last few times it happened, I pulled over, shut off the truck, then immediately started it up again and it ran fine. Again, I slowed down to pull in my driveway and it started to run rough again. This is an intermittent problem. My mechanic said there were misfires in cylinders 1 & 3 and changed all the ignition wires and basically did $400 worth of work. I'm getting codes P0303 which means cylinder 3 misfire and P0455 which means evaporative emmision control system leak.What's up?

 

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