I have a 99 Cav coupe (base model) with a 2.2 and 110k miles. When I'm on the highway and traveling 68-75 MPH, the car begins to bog and the temp gauge falls and then rises. It almost feels like I'm stuck between a gear, but the problem is definitely not the tranny. The car runs fine when I'm traveling below 68 MPH or above 75 MPH.

A few months back, I had the same issue at a lower speed (55-60 MPH), but the spark plugs were changed and the issue was resolved at that speed. Could the issue still be the spark plugs?

no idea, i would try changing the wires

holy cow i had the same exact thing!! i changed plugs and wires and it fixed it.... i'd check that and see if it helps.... now my temp gauge is acting up again.... ugh!! i just need a new car