As xulfiqar suggested, get the coils checked.
Do you drive at 120 in the motorways? From your description I feel you do.
From my little experience, you're probably demanding too much from the tiny 660 engine. These are not meant to be driven on 100+, especially with AC for long stretches.
While you're getting the coils checked, do get a compression test, and compare results to the service manual/another vehicle. And also see if the engines consuming any oil.