I have a 2013 (6-speed) and a 5000# trailer. Had a chance to tow it for the first time last weekend. My LC setup is currently stock (no lift, no re-gearing, and no armor). The trailer is 8' wide, 9' tall, and 23.5' long (including hitch), dual axle, and runs about 600# on the tongue. I run a WD hitch and a single anti-sway. When I pulled my trailer over the weekend I had a WiFi OBD2 reader attached and was running EngineLink to read the data. Here are my thoughts on towing with my setup... I know it's a 2013 but my results should generally apply to your setup as well.
Limiting to 4th (In the 2013, 4th is 1:1, IIRC in the 2016 it's 6th) I was cruising at 65-70 in mostly flat Illinois/Wisconsin (I-94) and ran around 2800RPMs +/-. I got ~10.5MPG at that speed (the instantaneous MPG reading from OBD2 was pretty steady between 10.2 and 10.8MPG). I tried running in 5th for a while but I found I had to lay into the gas pedal more to keep it at 65, so my gas mileage actually went down. Unless I was driving 55, using OD provided no MPG benefit.
I also watched the temps closely during the trip. Outside it was ~65F out. Intake temp was reading about ~90F (typical). My trailer was at the shop getting the bearings repacked so I drove about an hour to pick it up and then about an hour after I hitched up, thus I got some great comparison #'s:
- Without a trailer running in top gear (6th) the transmission pan temp reached 195F (+/- 1F degree), and the torque converter was anywhere from 195F (when fully locked) to about 208F (for instance when accelerating from 60-70). The higher TC temp didn't affect the pan temp much. Once the TC locked up again at ~70MPH the temps would both stablilze around 195F again.
- With the trailer running in 4th gear the pan temp stayed around 196F (+/-1F). Both the TC and the pan temp would read the same when cruising at 65MPH. About 2/3 of the way through the trip I tried running in 5th gear (first OD). The TC temp would climb (at one point it hit 213F) and the pan slowly climbed up to about 202F over the span of about 5 minutes before I put it back in 4th. At that point the temps slowly dropped down to 195F again. Also, I definitely noticed the weight of the trailer a LOT more when towing in 5th than in 4th.
In short, don't tow in overdrive - the gas mileage difference is small and OD generates heat in the transmission, especially if the ambient temps are warmer and/or you're pulling through hilly terrain. Yes if you're pulling a 2000# 4x5x8 uhaul trailer you can probably run in 5th or 6th without any damage, but if you're pulling a smaller trailer running in your 1:1 gear (6th in your case) will have less impact on your MPG than it does for me, so the $ savings is minimal.
As a side note, the weight of my gear (cooler, dog, etc) and family sinks my rear by about 1.5", and the trailer reduces another 3.5" (even with weight distribution running 4 links). I ordered a set of Firestone 4164 help air bags for the rear and an Air-lift compressor kit when I got back home on Sunday and am going to have my mechanic install them next week (I'd do it myself but I don't have a place to work on the truck except a cobblestone driveway that isn't completely flat - terrible for jack stands). I plan to write a full post on my towing experience in a couple weeks once they're installed and tested.