Just bought a 2010 F250 Super Duty Turbo Diesel last month with 7,500 miles on it. I plan on using it to haul a 18' tandem trailer max weight 5k lbs. With advice from a friend I added two up grades (SCT Livewire Flash Tool and a Bully Dog Cold air intake) to improve performance and fuel mileage.... My question is should I use the tow/haul feature or normal transmission. When I don't use the tow/haul my RPMs are around 1500 at 55mph and under 10 psi......With the tow/haul it stays around 2000 rpms and 10 psi.......I'm getting 14 mpg with the trailer and 24 mpg without with the upgrades.......Sorry if this is a stupid and long winded question...Newbie here...lol
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congrats on the new truck!! and welcome to FTE!

my opinion on tow mode is use it if the transmission is hunting for gears (keeps shifting) usually on hills this will happen. I also like to use it on downhills, makes holding a speed easier and less use of the brakes....with your trailer weight you could probably get away with not using the tow mode most of the time.

24mpg unloaded? you must drive downhill with a tail wind alot! lol

 

This mileage is highly suspect. Are you relying on the dash display? While accurate enough stock (at least mine is) they are notoriously bogus when you have a tuner installed. Hand calculate is the only accurate way to do it when tuned.

 

That trailer is next to nothing. Unless it hunts, leave the tranny alone.

Steve

 

I usually only use mine when I run through the northern Kentucky rolling hills. Like stated earlier, the ups and downs of hills. My trailer is slightly heavier than yours and I have a V10 so she is a screamin 3.5-4k RPMs bout 8 MPG specially when JO's get you bogged down and take away my run at it.

 

WOW I did as you suggested and was very disappointed with my results. Huge difference in the numbers...actually getting 13.1 with the trailer and I've not had the chance to calculate without.....So my dash read out is useless now???? bummer

 

+1 Do not use tow/haul unless you are in and out of overdrive.
+1 Tuners screw up your overhead mpg readout. Prior to my tuner my readout was within 2 tenths almost every time. Now it usually displays about 2 mpg better than I am actually getting.