2005 Other Jeep Models air cabin filter?

Is there a Air Cabin Filter in the model? Sorta likt an A/C filter in a house, and where is it? Also I brought this jeep to the dealership 2 months ago for a tune up, they say they changed out 16 spark pluds, with new champions, But we were getting an avergage of 17.8 to over 18 miles to the gallon around town, now its dropped down to 13.6, ive taken it out on the highway and blown out the build (which it never seemed to have prior to the now plugs, and that helped on a short time maybe for 10 days and now the m.P.G. Are back down to 13.4 there is a slight hesitation even if you put the pedal to the floor, I know it has the 8/6/4/ cylinders gizzzmo, but even putting it down in firt and or second gear it still has the hesitation, it, s a little scary pulling out into traffic sometimes, is it hard to remove the plemum to service the plugs and check the throttle body?Thank You Guy, s in Advance. Danny