85K miles, factory tires finally worn out, 1/32 in the rear and 3/32 at the front. Changed to Michelin defender at Costco, MPG: 41.3 ---> 34. Doesn't expect that much, will try to drive more to see. Pro: finally find out the alignment is way off at the front, much smoother maneuver now will see how MPG goes after couple thousand miles
I bought the same tires from Costco also. My drops in mileage weren't as bad as yours. It did take about 4,000 miles to get back to normal. I drive fast and avg around 45 mpg.
I guess I just wait until next maintenance then. By the way, I usually drive 79 mph on highway. It should decrease the mpg a lot. I tried once with 65. It really made a difference.