May upgrade our tow vehicle

[Sleeve66]

You should be able to get at least the 10 that you are looking for. If not then look in to a programmer and maybe an upgrade to your intake system. Or if you don't feel comfortable with playing with a programmer then it would be worth the money to take your rig to a diesel shop that specializes in aftermarket emissions.
I am running a 2000 Ford F-250 superduty 4 door cab long bed pulling a 37' Cougar SRX. I am averaging 15 to 16 mpg pulling it around Oregon and Washington. I have a cold air intake system and a Edge programmer. I run it in the tow mode all the time and it get's me the best overall performance. If you bump it up to the next mode it starts to blow smoke which is just wasted fuel.
If you don't have to take your truck thru annual emissions tests then it is worth it to have your egr and after treatment filter removed. Like I said talk to a local diesel shop, not a dealer to find out what you can do to get the best MPG. Good luck and I hope this may help you out.