I had owned both the 5.4 and two v10s over the years...the 5.4 was really pathetic in terms of towing mileage and performance. The v10s got as good or better mpg, and the power was amazing. My 05 six speed manual v10 got 16 mpg unloaded on the hiway....the automatic I owned before got about 13-14.
I recently bought a newer truck....I looked at everything and narrowed it down to a v10 and a GMC 6.0 gas motor. I thought the GMC would give better unloaded mpg.....it is crap. I have yet to see 14 hiway.
We had a 5000 pound trailer and I got 9-11 towing. We bought a new 7500 pound trailer and now I get 7 towing and the constant shifting is a real pain...
Story short, I am looking for a v10 again!!