Add a 3rd opinion. Perfectly OK. The oil is hot and thinned out by the highway run, and at idle the oil pump isn't moving very fast. It's probably an indication of a moderate amount of wear in the engine, you might have (shock!!) only 150,000 miles left!! If you do a lot of highway trips you might consider using synthetic or synthetic blend oil, it seems to maintain viscosity better when abused or hot. You might try switching to a -slightly- higher viscosity oil, but the benefits would be almosty completely mental.