Your right... what the manufacturer recommends is always the best bet. FWIW, I had an 02 Tundra (4.7L) before I bought my new one.... I always ran synthetic 5W30 and I pulled its guts out and never had an issue.
Re: What weight motor oil do you use in your tow vehicle?
For what its worth I run 0W-40 Mobil 1 european formula which is different from all the other mobil 1 oils as it is the only one that meets Mercedes Benz specs for my engines. (gotta read the fine print on the bottles) Also I only use filters with fleece type filter media. Changed about every 7500 miles