I really like the 5.4L as well, I read where many folks don't like to let it rev while towing in the hills. The modular motors love to work and generate HP and torque at much higher RPMs than we all are used to, so let it sing and do the work.
Here's an example of the new Ram from our neck of the woods, 6.4, 4x4, crew, towing package, etc.
http://www.jamesonealchryslerdodgejeep.com/new/Ram/2015-Ram-2500-bremen-atlanta-dd2747540a0a000261e288bd830e24d5.htmFor those of us who play with gears purely speculating:
A 5.3L makes 285HP @ 5,200 rpm and 325 ft lbs. torque @ 4,000 rpm. Most would suggest ideal towing (working in the hills) would be near or above 4,000 rpm (max torque) in whatever gear you were in.
To get that in drive, at 65 MPH with 235/17/16 tires and a 4L60E trans, you would need at least 4.10 gears (and then you would only be at ~ 3,200 rpms). Pull into 2nd drop the speed to 52 mph with a 4.10 and then your at ~ 4,100 rpms, right at max torque, and your engine should be pretty happy pulling the load.
If you're interested, you can play with the numbers on the calculator posted above, It was a real eye opener for me. and lots of fun as you can guess. I had no idea I was missing the max torque mark so much in my van, I now tow most of the time out of overdrive, (for rpms with 3.55 gears, in addition to conserving the trans), right under 65 mph (near my max torque number) quit worrying about gas mileage, since I'm really pulling a barn door down the road behind me anyway, and enjoy the ride. It made a huge difference for me.
4L60E gearing:
Gear ratios:
1 2 3 4 R
3.059 1.625 1.000 0.696 2.29
GM sticker codes
GU4 is a 3.08
GU5 is a 3.23
GU6 is a 3.42
GT4 is a 3.73
GT5 is a 4.10
More than you asked for, but I'm for fixing what you have if it is still in good condition and meets all your other needs.