I get around 24 mpg with my '15 Sienna AWD 2grfe (running 0w40) on highway trips. The coolant has about 25k on it, the air filter is clean and I keep up with 5k oil changes. No oil leaks thank goodness. Been doing a drain and fill every 25k on the U660F transaxle, rear diff and xfer case oil changed also 25k ago, had dealer do a brake fluid flush and brake pad check last Fall. Other than these items, and keeping the Michelin Defenders rotated on time, I can't think of any other preventative maintenance items to do before I leave. Can you? No water pump problems so far, so I am keeping my fingers crossed. Thanks.
Sienna is easy when it comes to maintenance. We did multiple road trips, 2000, 3000, 5000mls.
The issue with Sienna is following:
1. Aggressive driving will obliterate rotors. Rotors are for grocery getting. If you are not loaded or pushing it, they will do it. They warp. It does not matter do you have 1000 or 10,000mls on them. They are small and made of cheap material (I am talking OE Toyota). I upgraded to EBC rotors and the problem was solved.
2. Clearance. We got rid of our partly bcs. we could not access some cool stuff in some national parks. It was also AWD, but too low.
I would not be worried about mechanical stuff on Sienna. Engine and transmission are the best part of the car. It is other stuff, overall quality, that is an issue.
This is what happened to me on the road trip:
If the tailgate hits an obstacle, the hinges are going to bend. There is no maybe etc. they will! They are too small and weak. Be careful when lowering the gate, not to have an obstacle. My kid pushed the swing bike rack, I did not see it, and the tailgate hit it while lowering. It went back immediately, but it was enough to do this. This was 4 years ago, and back then, a tailgate, without any accessories in it etc. was going $3,200 before labor, moving subwoofer etc. Total back than was around $5,000, which, of course I did not do it. It is such a common issue that the local dealership has a bunch of tailgates stocked in the warehouse. I fixed it temporarily and sold the vehicle to a local Toyota dealer during crazy high used vehicle prices.