I just bought a 2008 f450 and i dont notice the tranny shifting when i engage or disingage the tow / haul , maybe it is something new , my other trucks all of them switch RPM,s , when im going 60 mph im hitting 2001 rpm,s i know it matters what gears i have in the rear ,, but i think my tow/haul is stuck in the on point , the gauge on the dash works ok ? help

You may be thinking of the older Fords that had O/D on the end of the shifter...Tow/haul is not the same
With the gears in a 450 {4:88 i think} you will turn alot of Rpms

I have an 08 with 4:10 gears. A little less tow rating but it was enough for what I intended to tow. I think it does change the shift points but still allows you to shift into overdrive, just at a higher RPM.

The biggest thing you will notice is the downshifting when you are braking with the switch in the tow haul mode. The trans assists in braking.

How much does your 382 weigh on the trailer and how does the f450 pull it?

I found a 2008 F450 King Ranch 4X4, Nav, Sunroof 10,700 miles i can pickup for $39,000. Is this a good buy???

Yes!

ok... i hope this dosent offend or make me look like a dick but this is right out of our shop manuals. (i am a ford diesel tech)

Tow/Haul

The tow/haul feature was designed to assist the driver when towing a trailer or a heavy load. All transmission gear ranges, including all 5 forward gears, are available when using the tow/haul feature.

The tow/haul function is activated and deactivated through a switch located on the end of the selector lever. The indicator light that is located in the Instrument Cluster (IC) will illuminate when the tow/haul is activated and will go off when deactivated.

With the tow/haul activated, the transmission will have the following features:

Shifts will occur at higher vehicle speeds for a given Accelerator Pedal Position (APP) to improve vehicle acceleration, reduce excessive shifting and increase the coast braking capability.
The torque converter will lock up at lower vehicle speeds than normal with a given APP to improve transmission cooling and efficiency.
Upshifts are temporarily delayed while decreasing APP during hill cresting to reduce excessive transmission shifting and to prepare for a possible grade braking downshift event.
Engine braking is provided in all forward gears without the requirement of moving the selector lever.
Manual 1, 2 or 3 will still be available.
Grade braking downshift feature provides increased coast braking automatically to assist driver in maintaining desired speed while descending a grade. This reduces duty cycle on the brake system and increases brake pad longevity.
Grade braking downshifts are automatically commanded when:
positive vehicle acceleration is sensed (natural acceleration from grade descent).
a near zero APP is obtained.
a minimum amount of time has expired since the last grade braking downshift.
Grade braking downshift mode is immediately exited should the tow/haul mode be deactivated or if the accelerator pedal is pressed beyond a minimum threshold.

Make sure it has the 4:30 gears and not the 4:88.The 4:88 will kill you on fuel.Mine has the 4:30's and I am seeing 13 on the highway and 11 in the city.That is a smoking deal for sure.

Yeah, but you drive like an old man!

On a serious note, I assume those mpg numbers are without the Beak?