i'm not a car person but i would be willing to bet that driving long highway miles is actually easier on your car then regular city driving.
There was a stat yrs ago that stated that the Ferraris that ended up on tow trucks were the ones that sat in traffic all day---their owners never took them out to "air out".
City driving is worse than HWY driving, as the stop and go puts stress on all the systems. I've had all my breakdowns due to city driving.
With 98k, your car has just been broken in.