I've used a 1999 5.4 on my camper and cattle trailer, went ok but not too much power, and only 4 speed transmission so big range between shifts in tow/haul
looking at either a 2008 8ft box vs 2009 6ft box, both with 5.4's, will I see improvement with 5 speed transmission or am I better to look for a 6.2l 6-speed?

 

6.2l if your trailers "loaded" are over 7K will be a big difference in power. 6,2 is just a better choice all around if you can afford the gas....

 

There really is no comparison between 5.4 and 6.2. The 5.4 is a fine platform but the 6.2 with the 6 speed transmission out performs it plus the extra horsepower doesn't hurt either.

 

I have a pair of 150's. A 5.4 and a 6.2. The 6.2/6 speed is a real towing machine as gas trucks go. The 5.4 is no slouch but the 6.2 has better power and more gears, so it's kind of a no-brainer for me. The gas mileage is just about a wash between the two.