Have recently purchased 2005 F-350, crew cab,4x4, V10, 4.10 gears, 125k, etc. First time using to tow was just small trailer and utv, with gear in bed. Trailer and utv prob 3500lbs. Prior to purchase, read up on towing, with everyone's saying how good they tow. Besides gas mileage, it was said they were good for power. Towing from phx to Flagstaff, and small trailer, some grades 4000rpm, 40mph? Temp 103. 1" taller tire 2" leveling kit, new air cleaner, new fuel filter, and switched to 08 pan, as I saw was good upgrade. Seems like older 2500 chev 6.0 did better, with 60 less hp, and 100 less ft lbs torque. What am I missing. Want to tow toyhauler same route later, but thats 5k heavier. ???

 

You might want to repost in the V10 subforum: https://www.ford-trucks.com/forums/forum49/

 

I pulled 11K pounds dozens of times from Phoenix to Flagstaff and back with a 2 valve V10 with 3.73 gears and 35" tires and could maintain 40mph. The hill coming south out of Camp Verde was about 35mph, that was because if I went any faster the transmission temp would get too high. ????????????????????

 

That doesn't sound right at all, I tow my 13K lbs toy hauler up very steep grades all the time and don't get under 50mph. I am running a 4.40ish equivalent gear but it should make that big of a difference. If I'm towing my RZR and utility trailer which is around 3500lbs it doesn't go under 65 ever. Have you checked the plugs? Any service records for the transmission? I do run a 5star tuner and couldn't imagine towing without it anymore, the transmission schedules are unmatched.

 

Trans pan upgrade to 08, works good and not getting hot. Prob do plugs this week, prob never changed.

 

I had 08 dually 3v V10 with 4.30 gear pulled a 12k 5th wheel all over the US, climbed mountains through the west. RPMs are your friend with the V10, if you where doing 4,000 @ 40mph on a climbing grade that's good. I can recall hitting some Colorado mountain grades @ 5,000 rpm doing 25-30 mph, won't win races but it had excellent steady power.

Keep the tow button engaged and use the shifter to select a lower gear on the climbs. You won't over rev the engine it has govenor for rpms, 5,000rpm I believe.

 

Was that all she's got? You can rev that V10 to around 5500. I've towed up and down Hwy 87 to Payson (2 quads on a rack in the truck and 6500# travel trailer) several 6-7% grades, around 4600-4800rpms and 50-60mph. Foot is pretty much mashed to the floor.
I have a Trutrac LSD and plan on 4.30 swap soon.