I'm with The Sequel. All of my miles are highway and I do the oil at 5,000. I just did my coolant at 50,000 (don't scold me, please) which was a few months shy of two years. I managed to get 5 gallons out of the system so I got a good change. Next, I plan on flushing the brake fluid. I did the rear end at around 15,000 and went back with synthetic. When I can get the lube, I'll do the transmission.