Your trans temps sound perfectly find for where you have the sensor. The test port is around the same temp as the pan. Like Diesel_Brad said, just lock out overdrive it if starts huntin between third and overdrive... every time the trans shifts there is slippage in the clutch packs just like any other clutch and this will build heat fast. I just towed my buddy's Chevy K1500 home from the local mudhole yesterday (maybe 1/2 mile on trails after pullin him out, and 4 miles on the road) and my trans temps in the oil pan didn't hardly break 170. Factory radiator oil/water and oil/air coolers, nothing else.

And yeah, 3.55 gears = not so good for towing. I know because I have them. She did fine, just a lil sluggish gettin up to speed but I was fairly easy on her and did about 40 MPH, speed limit was 45. No need to make her work hard just for a few more MPH's. My F-250 had 4.10's, big difference with that and the 460 with a load behind it.

Don't try to go faster than the truck is comfortable with, remember the brakes ain't as good as they are on that 06 Powerstroke, keep an eye on the trans temps and you'll be just fine.

 

Iv towed with 3.55s... I think thats what made me unimpressed with my 460 initially lol. But iv got 4.10s waitin on me! Just need to scoop up some cash.

When I hauled a race car, I had a hard time deciding which gear to choose. At about 60, it downshifted at a slight incline. So I had the choice to slow down some (to keep rpms down) and OD off, or speed up to 65 with OD on. I chose 65. Boy once its up to speed, itll hold it well! Only once did it downshift twice. And again, I live in the plains lol. We have small hills, not mountains

 

yea if i can get some extra money saved up i might try and go with some 4.10s. i had them in my last truck a 96 with the 351. so i have an idea of what they feel like. i also have them in my mustang. when i put them in my car i just did a whole rear swap. i dont want to mess with putting gears in my self.

 

Thats what Im doin with mine. My gfs uncle is building a pulling truck and didnt need the entire drivetrain out of his truck. Made me a deal I couldnt refuse! Comes with 4.10s, LS rear, ZF5 and a spare engine. Plus everything else incorporated in a drivetrain lol (missing on one cylinder but I have big plans for it anyways )

More torque plus 4.10s means itll be a towing MACHINE!

 

My CCLB 460 with 5spd has 350s and it's great. But it's not an auto, and it's not stock. LoL
My xcab lb has 410s and e4od. It is mostly stock, and tows 10k great. It's all the little things that help a lot when added.
I'd reccomend semi synthetic or full. Either trust me when I say go 7k miles per oilchange or get an oa done to determine change interval. (I can go 16k on my psd and 8800 on one of my 460)
I would also swap out all fluids with synthetic (not royal purple, it has oxidizing issues)
Even though my truck don't have 60k yet, the fluid wasn't the best. The age and condensation gets to the fluids and iffy things happen.
The 460 needs a little more fuel pressure. I've crushed them before but now I buy adjustable regulators. Tweak base up to about 46 without vacuum. Try that and go up until it gets fumy. My truck loved it. Bigger fuel pumps don't hurt. Stock I had a pressure drop on big long hills where I was in the throttle hard. Coulda been weak pumps though. One truck got a lightning (supercharged) tb and no cat, diesel exhaust.
Hmmmm. What else. Lots to do so it tows better without swapping gears.