towing fuel milage

As stated in op the trailer is very small, I pulled it over 20k with a 4 cylinder Chevy Colorado. The current truck is rated to tow 6000 lbs. Power is know problem. I just expected better mpg. I've been towing small trailer with 4 and 6 cylinder trucks since 1990!

Sounds normal but is it really a problem? What percentage of your miles are towing vs your other use of the vehicle? If you did a 1000 mile trip at 10 mpg vs 13 mpg the difference would be about $47.00 Not enough to worry about if the vehicle does everything else well.

As donno said, your axle may be a big part of it. What is the mileage when not towing?

I had a 1999 Silverado plain Jane truck with a 4.3 and ran the snot out of that thing for 225,000 miles. I did replace the intake gasket and water pump at 160,000 but it was a fantastic engine. It still ran excellent when Obie gave me $3,500 on the cash for clunkers deal.

I also had a 2013 Silverado 5.3 with a 5,000 Jayco TT that got 10 or 9 at times.

I now have a 2014 CTD that's doing 22,000 gcw and it gets 10 to 11 but empty at 60 it gets 25

^ baloney. Clearly someone who never drove a 4.3.

OP- fuel mileage is mostly determined by wind resistance. And no, it won't improve I you get a bigger truck. 10 is not unreasonable.

Too much weight, not enough motor. And probably the wrong rear end ratio. You bought yourself a fancy grocery getter with an open bed in the rear instead of a real truck to work with. Can you fix it? Maybe, but IMHO you would be better off trading for a more capable truck.