If that 5500 lbs is the loaded weight and you want a little more oomph I would seon the vote on the 3.73's. If the 5500 lbs is the empty weight...welllll...that would put you at 6500 lbs or so, a little heavy for the Expy.
The 26' Mallard that we towed with our 2000 Expy weighed at 6200 lbs loaded and it was a handful for that truck with the 3.55's, lower gears would have definitely helped. I added air bags and was getting ready to go down the road of the Banks power pack with hi flow exhaust and tuner when DW informed me after our 1800 mile 2 week road trip that "ever since we got back from that last trip with the trailer the truck is shifting funny....".
Woke up to the realization, and as was mentioned in this thread "it is what it is". The 5.4 is a strong motor but not cost effective to try and wring more power out of it, and if you did, it would toast the transmission. Friend with an 02 Expy toasted 3 transmissions towing their 28' UltraLite trailer.
Best thing you can do for your Expy at that weight is add a transmission temp gauge so you can watch what's happening when you are towing.
