I don't own a Hemi nor have I ever, but I have to wonder if your truck is running properly if it is struggling that much with 5500lb behind it.
Other members here tow much more than 5500lb with Hemis and I don't recall reading too many posts regarding unsatisfactory performance.
Do you track your mileage? I have to wonder if there's something (clogged cat or fuel filter, overdue for a tune-up) holding your truck back from its full performance.
I track my MPG mainly to watch for a sudden drop in economy which would indicate a component not operating efficiently.
I politely disagree with Slated4; I've been there, done that with intakes, exhausts, chips, tuners, etc. and in my experience they make very little difference and can actually have negative effects (voided warranties, dirty intakes, loss of low-end torque, additional engine noise, etc)
