ive pulled a double axle car trailer with a 2500 4 door duramax on it....sure it was very heavy but she did her not to bad.

 

I pulled an 18' tandem axle trailer with three large atv's on it from ohio to west virginia and back through alot of mountains and everything else, I did 70-80 on the highway and got about 11-13 mpg,and I wasn't revving nearly as high as you say you were.

 

Mine doesn't struggle too bad towing over 7K. I think your tranny is shot or something. My heavy duty 20ft trailer weighs 2700lbs empty and my truck will *&$% and get it empty. Got 15.5 mpg on the highway towing it.

 

My 2004, hemi, 4x4, quadcab,3.92 gears, air bags, pulles my 26 foot, 6,200 lbs empty toyhauler (then add water 150 gallons, 5 dirt bikes, 1 atv, wood etc) and I can pull down the highway in 3 gear at 65 then it shifts to 4 gear and will drop down to 60-55 (2,00-2,500 rpms). On hills 2 gear, 45-50 mph at 4,000 rpm.

Ooops, Dodge is rebuilding the rearend for the second time, 51,000 miles.

 

Maybe you hit the nail on the head with that one.
The trailer doesn't have any brakes on it. It was sitting at an incline because the hitch I think had a raise on it, or sat flat.
What makes it worse is that I towed the same trailer with a ford and a mower on it, and it didn't do too much better. That was just a big kick to the ***** for me and my truck.
I don't tow much, so I don't need a 2500 or anything bigger, but I will pull a trailer when I move away for college.
If my tranny is shot, would you suggest rebuilding it? I don't plan on keeping the truck for too many more years though.
But yea, I don't think it's a problem with the trailer, has to be the truck.

 

I would have a reputable shop check it out. If you catch it early, it may not be so costly to go thru it because the hard parts can be saved.

 

What are some of the best telltale signs of having a transmission going out?

 

Dark, burnt smelling fluid. I would check it first. Should be bright red or pink, not dark or brown.

 

did this trailer have a ramp if yeas lay it down on the trailer
it makes such a huge difference. check the obvious like
brakes and bearings. 5300 are you sure its 5300 or 3500
either way something is not quite right here the truck should
get a once over.

 

There are ramps on it, but as I said before, I've pulled this same trailer with an extended cab Ford and GMC. Both pulled it just fine, and the ford has almost 200,000 miles on it. GMC has about 30,000 miles on it. So my truck shouldn't even need to have the ramps down. Yes, it was 5300 rpm.