Ford says 10 is fail-ing and 15 is fail-ed. With a trailer you'll properly see 13-14+. I'd start preparing for an oil cooler. I've diagnosed and monitored thousands of these things for oil coolers. A good cooler will follow your ECT all the way up to operating temp, wherever it ends up being on your truck, and should stay within 3-4 degrees unloaded, 6-8 while pulling and pulling hills. The excursion I just bought for my wife a couple weeks ago sits at 192 coolant and 192 oil at 75-80 mph for 60 miles straight. The cooler is simply a heat exchanger, and does not care what temps are. It always cools to the best of its abilities. Call it my opinion, but it's an opinion based off of literally hundreds of trucks that I have diagnosed a failing or failed oil cooler, replaced it, and on test drive have a 0-2 degree split whereas prior to the new oil cooler it was 10+ (up to 50-60). Your thermostat is slightly bad, the truck should be 192+ however that WILL NOT AFFECT the oil coolers abilities to cool whatsoever. With that being said, plan on doing an oil cooler and thermostat in the near future, maybe before it gets too hot outside.
06 King Ranch
Fass 200, Custom fuel lines, 225/100s, Thumper stage 2 hpop, WPE stage 3 intake, Mishimoto radiator, Flex a lite fans, BPD water pump, MPD oil cooler relocate kit, Intercooler pipes, Compounds built by me, etc etc etc
05 Eddie Bauer
Resealed entire motor @ 170k miles, new lifters, 6.4 push rods, studs, rebuilt the turbo, IPR egr delete, new injectors, new heads, new ficm board, coolant filter, intercooler tubes, regulated return, bunch of other new parts. Factory exhaust, cat gutted(wife's rig). Livewire with gearhead tunes. Should go a while reliably for her!
03 LB7 duramax the "daily/tow pig"
Lbz cp3, s475/stock twin kit, built trans, steel driveshft, amsoil bypass, secondary oil cooler built by me, fass, traction bars, trans cooler upgrade, dual alts, straight center link + tie rod sleeves, efi live, transfer flow/tool box tank, 5er hitch, other small upgrades.. and most importantly, STOCK HEADBOLTS! Just rolled 200k miles, twins installed @ 165k, daily driven on a "550 tune" tows 18k on a "475" tune.