The 2012 Liberty was only available with the 3.7L V6, rated at 15mpg city and 21mpg highway. Glad your ages such a high mpg with your trailer. That's impressive.
Just as FYI: depending on equipment the Liberty is rated in the US to tow up to 5000lbs. Since its less than zippy by itself I'd think its even more sluggish with a trailer behind it.
My Wrangler tows my A126 fine, but its sluggish. Factory tow, plus an auxiliary transmission cooler.
2011 FR Rockwood Premiere A126 Hard Side
TV=2011 Jeep Wrangler Sahara 2 Dr
Reese 66065 WDH, Curt WDH Shank #17120
Prodigy P2 Brake Controller, Mopar 7-pin Harness
B&M Transmission Cooler (#70268)