2000 LS using oil... sometimes

I have a 3.4L engine with 130,000 miles on it. I can drive 2,000 miles on an oil change in my normal stop and go/occasional highway driving habit at home, check the oil, and its only down a quarter of a quart. but if I take a road trip that's 450 miles each way, all highway, I use almost a whole quart just going one way.
I noticed that the butterfly in the air intake gets some oil and crud on there pretty quick.
Driving on the highway I usually set the cruise at 70 the whole time leaving the engine running about 2000 RPMs.

what could be causing more usage just from driving on the highway?

thx for any help!