That's not unusual given the ambient temperature. Same here for me in MN, on average. I just had my t-stat done on my '11 X5D back in early December. I live about 20mi outside of downtown St. Paul, and ran at about 84F for most of my commute home yesterday, at 40ish F ambient.

Just keep an eye on it over time. When it starts to fail, you'll likely not even hit 80F. Even running hard for highway trips in DS, I couldn't get past 78F before I had mine replaced.