If you chose to change gearing, most people (outside this thread apparently) recommend at least two steps. So, 3.55->4.10. 3.73 is not enough of a change to warrant the money invested. The difference will be noticeable, but barely.
I had a 2003 F-150 2V 5.4L, 4-spd, 3.73. It did well, but I always though 4.10 would be perfect for the engine/trans, running in 3rd gear towing my TT.
I caution people changing gears. I think it's the best bang for the buck for towing. However, that's $1500-2500 for 4WD vehicles that you'll never get back on a 13 year old vehicle that might be worth $8k. It's often more valuable to just find a different similar vintage vehicle with more capability.
