Instead of low and slow like the old low riding days, your's is tall and slow Those are your options, gears- with no real added power boosters, the gears will multiply that, or more power and a new tranny...I'd go the more power route!

 

I had the same problem on my 06 Megacab 2500 auto, 4X4, 6" lift, 37" tires, with a muffler delete. The truck went from hauling a**, to running like a ford ranger with a 4 banger in it after the lift kit and larger tires.
I installed the Diablo Predator tuner and a boost fooler. I have ran the truck on tow pulling my boat and also when pulling a 35' fifth wheel toy hauler with no problems, and run it on performance for around town driving and when only needing to tow the boat. The truck now has aswesome power, gets up and has plenty of passing power now. I am happy not changing the gearing as that was my original plan. Before the tuner install, my mileage dropped down to 14 or so with the lift kit and larger tires. I am now up to 18 or so average in town and freeway driving hand calculated.
I would go the tuner route, but do not leave it on kill. The auto tranny will not last.

 

You definately need to do some upgrades!! Chip, air intake and exhaust will help a lot.. I had a 6" with 37's and 20's on my 05 and towed with ease!!! I wouldn't change gearing at all as I had 3.73 and got 18-20 all the time towing or not!!

Here is a pic of my trailer and old truck..

 

Thats kind of my deal, I love the look of my tires but I also want to get something out of them. (or at least fool the warden into thinking theirs an upside) Thats why I didnt change my gearing. At highway speeds my milage is very good, if I change the gears it would suffer. Also I know me I only keep the truck for a few years and I can pull the tires and put them on the new one. If I had to go back to stock tires with a different gear ratio the truck would only go 55 and sound like its gonna blow.
Either way they are both good options, heck do both then youd have a monster.

 

With the BD Triple Dog Ive found my power and few extra MPG...Thanks for all the thoughts/suggestions...

 

Go to the dealer and get your pinion factor reset for the larger tires.
You should not notice a large decrease in power.
My guess is with the bigger tires, your tranny is shifting like poop.

 

I have 4.56 paired up with 40" Toyo's I have no problem burnin the rubber off and with the 4.56 gears speeds of 90mph keep me in the 2k rpm range

 

I wonder what my gears are at with the 3.73 and the 22.5 but I like it but I do have a 6spd.