Toyotas can get rusty I would check out the condition of the underside and the service records John mentioned. On the rust topic, something as big as the Tundra likely didn't live inside a garage The sub frame on our '06 Rav4 was completely rotted out (it's spent its entire life in CT and has never been garaged for any meaningful time), and I wish I had take a picture of the backside of the rear knuckle before I started braking chunks of rust off. And the rear backing plate literally disintegrated in my hands yesterday when I took the hub off. Literally every part of the subframe job has been a huge pain due to the overall rustiness of the vehicle (bolts snapping, driveshaft rusted to the coupler, bolts rusted inside bushings. I don't know how many (if any) pieces I'm going to be able to reuse, which will definitely add to the cost of the job.
What's the list look like on the current truck? I generally fall into the devil you know camp (as proven by the work above), but I've also recently rehabbed a 2017 Odyssey bought a year ago with 193k on it (and no service records) to the point where I trusted it to take it on a family vacation down to FL (the alternator died on our second day down there). But I did a ton of prep prior to that, which might be similar list to what you'd be undertaking on the new truck to ensure it's a reliable tow rig:
- Timing belt/water pump (not sure if the Tundra is a belt or chain)
- Radiator/expansion tank/thermostat/hoses & clamps/fresh coolant
- Transmission fluid changes (3x), replace OEM transmission filter, add aftermarket transmission cooler, 2 new factory ATF lines (both were leaking)
- Valve cover gaskets (they were leaking), spool valve gasket (was also leaking & was ultimately what killed the alternator), valve adjustment
- New serpentine belt and pulleys
- New rear shocks, new spring bushings, AirLift airbags in back
- Replaced passenger side wheel bearing, drive axle, and drive axle seal (it was leaking)
- Installed roof rack and crossbars
- New tires
- New brake fluid
- Alternator and battery (failed while on vacation - I had a local dealer take care of it)
Now that the thrash of the past year is over, it's in a much better spot. There's still odds and ends and regular maintenance that needs to get taken care of, but hopefully the volume of work remains low.
Edit: here's the back of the knuckle after spending 15 minutes knocking rust off: