I would confirm what Brad2 says. I have my original Michelins on my 2010 RX350 AWD and at 88,500 miles, it was finally recommended by my dealer to look at replacing these.
I have had my 2010 RX350 for a little over a month now. Approx. 60% of my driving is highway. Overall I am averaging 19 mpg with 22-23 mpg on my trips at 70 mph.
I saw a deal on KBB for a Denver CO dealership offering $3,499 down and $389 a month for a 36 month lease, 10 miles. My dealer in KC matched that offer.