"I've got a brand new F150 5.4 Triton that calls for 5w-20 as well. I plan on using it....and I will tow with it as well.
I recall reading snippits here that imply that todays 5W-20 will remain a 5W-20 after 5,000 miles, where yester-years 5w-30 will shear down to a 5w-20 in the first 2-3000 miles. Engine tolerances are a lot tighter than they have been in the past as well which calls for a thinner oil."
The Triton was launched in 97. Mods were made to the top end in 00. I can find no evidence that tolerances are tighter to require a thinner oil. The 5-20 is a CAFE ploy to gain increased mileage across the board at Ford, as well as other manufacturers. You can use the 5-20, but if you are towing in hot weather, or overheat, the oil film may not be enough to protect. As usual, the choice is yours. For maximum engine life, personally, I lean toward a slightly heavier oil, always. OTOH, I expect over 200,000 miles from each of my cars.
Here is a quick quote...
" Since its launch, the Triton engine design has proved versatile enough to power the F-Series and Ford's full-size SUVs, yet fully pleases the core market. It pleases Ward's, too, as this year marks the Triton's fourth consecutive year on the 10 Best Engines list.
Last year, Ford engineers reworked the Triton's upper end: The camshaft profile was revised, a larger exhaust valve was specified and the cylinder head casting was redesigned to promote improved tumble motion of the intake charge. The net result was a solid 25 hp, bringing the total to 260 hp. A competitive number, but not the best horsepower rating, which can be a liability in the dog-eat-dog truck market."