I have a 2006 F350 6.0 DRW 4WD CC which I love. I bought the truck before I sold the 2002 F250 7.3 SRW 4WD CC for towing our 37' 5th wheel.
On the way home from picking up our 5th wheel from being repaired and towing for the first time with our new truck, the truck made noises that the F250 didn't make while towing. On level/flat ground, the truck drove like a champ. I heard unfamilar noises while going up and down mountain/hill grades of about 6%.
On the grade up (with tow haul activated), I heard a high pitched whine while doing about 55 mph. The speed decreased but the whine continued even though I turned the tow haul off and then back on.
On the grade going down (with tow haul activated), it sounded like the exhaust brake (or Ford equivilant) came into play and kept the truck from running away which was great but at the same time, it looked like the turbo was off (no boost reading) and the rpms shot up to over 3200 rpms. The noise changed to a high pitched roar.
I don't know if either of these two items are normal or not. I didn't have these noises/sounds on the trip going to pick up the 5ver which was over the same flat/level ground and also hills/mountains while not towing, they were only there while coming home with the 5th wheel going up or down a grade.
I took the truck into Ford and the diesel mechanic could not find anything wrong with the truck, even with a load. You guys have, been there, done that, on this forum and I would appreciate any assistance you give me.

 

On the grade up (with tow haul activated), I heard a high pitched whine while doing about 55 mph. The speed decreased but the whine continued even though I turned the tow haul off and then back on. This is the auxiliray fan activating... And it sounds exactly like a high pitched whine.
On the grade going down (with tow haul activated), it sounded like the exhaust brake (or Ford equivilant) came into play and kept the truck from running away which was great but at the same time, it looked like the turbo was off (no boost reading) and the rpms shot up to over 3200 rpms. The noise changed to a high pitched roar. The tow/haul feature takes some getting use to- Sometimes you need to press the gas pedal to go into the next gear.
I don't know if either of these two items are normal or not. They are both completely normal... Good Luck

 

What you were hearing was probably the fan kicking in. The new 06' is programmed to activate the fan to keep engine temperatures under more precise control.

I had a simular experience with my 06 f250 when climbing a long grade near Death Valley. It was not particularly hot (around 75) and near the summit I hear this whizzing sound and I thought it was the transmission. The sound would come and go, maybe lasting for 5 or 6 seconds. Anyway, after researching I learned that the fan will engage frequently and even off road in 4wd at slow speed. Nothing to worry about.

 

Yes, having the tow/haul on going downhill does cause it to feel a lot like an exhaust brake. That is because part of the T/H strategy involves the turbocharger. Basically, what it does is dial in the maximum possible backpressure, which makes it very much like an exhaust brake.

The noise on the uphill is probably the fan, especially if it goes in and out on your way up. The in and out thing is the giveaway, and man can it roar when it puts its mind to it! The computer controls the fan speed on these trucks even though the fan is driven off the engine. The bigger the demand on the engine, the faster it will make the fan go. The fan on the 6.0 is huge for a pickup, so it can make a lot of racket.

 

It's a relief to know that the noise is "normal" and that there is nothing wrong with the truck. The truck is great and does what I bought it for, towing my 14.2k 5th wheel. Does the fan sound ever go away on one of these climbs or descents or do I just roll the window down, listen to the sound of my diesel humming along and turn my radio on? Thanks for the replys. I have been reading this forum for about 18 months or so and it is great.