Jeep Liberty

I unknowingly had two different size tires put on my 2002 Jeep Liberty Sport by a dealership. In the year that my car had these tires, I had issues with the four wheel drive and also the engine. I know that the 4WD was a direct result of the tires, but I am trying to pinpoint the engine trouble. The car started running rough and then immediately just died on the side of the road. It would start but wouldn't hold idle and then would shut off again. I was told that it was a blown head gasket that caused the engine meltdown. Can anyone shed some light on my dilemma?
August 23, 2007.

What size motor?

Any prior problems?

Any check engine light?

Were codes pulled. If so what are they? IF not please do so.

Was the head gasket problem diagnosed? Or suggested?

I am not sure of the engine size, but I did have a check engine light which they diagnised as a gas cap leak. The head gasket was what they diagnosed, but is that something that may have been caused from the stress of the different tires and the 4WD?

Aug 23, 2007.
Unless there is somthing I'm missing, I see no relationship between the tire size and the head gasket. Ask them to explain just how exactly that could be.