I had the same problem. My car has around 90k miles & few times when driving on the interstate uphill my car would hesitate, almost like a stutter, then the check engine light would come on for a couple of seconds and I would smell a funny smell through the vents. I took it to my mechanic who could not find anything wrong with it because the check engine light would not come on for him. He put a type of fluid additive in my transmission which seemed to work for a few months. He also cleaned the undercarriage. It didn't do this that often so not really sure what was the cause. My mechanic suggested putting Seafoam Fuel Treatment in the gas tank. Didn't have a problem for a while and then my AWD Disabled light began coming on and is now staying on, so I'm not sure if there is any relation with this issue or just a completely different issue. My car still sometimes stutters but so far it is not triggering the check engine light to come on and I am not smelling a funny smell.