This is very strange.

When towing our 27FT TT (6000#'s) I got max 12.8-13 mpg tops.

Just did a round trip for the weekend with our 31.5 ft 5er (9500#'s) and got 14.9 mpg and at one point I was getting 15.5. (then I got in to stop and go traffic)

Only difference i can figure out is that I never got over 2K RPM or 70 mph. Most of the time I was between 65-70.

I am scratching my head.

 

Headwind...tailwind??

I know in my '92 F150 with the 300 straight six, if I pull an empty 3500# equipment hauler flat bed...top speed into a headwind was 55mph, but on the return trip...empty with a tailwind 85mph was easy.

 

Winds were "calm" today. Strange for DFW

 

WOW! I wish I had gas mileage like that. I was pulling my 8.5x16 v-nose enclosed with my Elise up to Virginia International Raceway and only averaged 9.5 mpg. Fully loaded it is about 6000 lbs. On Sunday I ended up driving about 4.5 hours each way up into the Smokey Mountains to go rescue a friend and his Miata when his clutch master cylinder let go. On one long hill we could only manage about 35 mph in 2nd gear with the pedal to the floor. Again I only managed about 9.5 mpg. It is going to be a long haul at the end of August going from Charlotte, NC to Aspen, CO and back for the Lotus owners gathering

 

Speed and trailer shape can have major affect - slower there's less wind resistance, a wedge nosed (or nose that acts as a deflector over the top) will help dramatically.

Running no trailer, I normally get around 13 running 72-74. When I went to Pennsylvania (2,000 mile trip) and keeping my speed at 65-68, I pulled 15. Didn't think it would be nearly that much difference, but I am driving slower these days - and dreaming of a PSD in the next truck...

 

I can get 17 mpg pulling a 3000# trailer if I keep it around 62. It drops to 14 if I run it over 70.

 

Although my trailer is only 8.5x16 it is at least a foot taller than standard as you can easily walk through the rear door without having to duck. It is a v-nose, but I think the extra height, the weight (6K loaded), and driving through the mountains is what kills it for me. I haven't checked my mileage recently though without the trailer. I probably should to make sure it is where it is supposed to be.

 

This is the answer right here! My 04 I just picked up got 15.5 on the 1st tank (no trailer) and I kept the RPM below 2K. The 2nd tank got crap as I was pulling a camper up in the mountains...didn't even run it as I knew it was below 10 MPG.

 

2007 SC towing a travel trailer that weighs aprox. 5500-6000 lbs. on mostly flat desert highway (2500 mile trip). Averaged between 13.5 and 14 mpg. Kept the speed at 62 and rpms at around 2500. Without the trailer I average about 15 mpg. I had expected a lot worse!
Went from So. Cal to Carlsbad NM, Santa Fe, Flagstaff, Zion Utah and back to So Cal through Vegas. Great trip, very impressed with how my new truck tows the trailer...

 

Makes sense to me, with just air drag being the difference. With the regular trailer, you basically have 2 vehicles worth of drag. One for the truck and as the air has room to come back down from over the roof to have full drag on the trailer front. With the fifth wheel, it is just an extension of the roof of the truck as it is so close to the back of the truck roof.

 

You have a diesel, right?

Sounds like normal MPG to me.