Over the last 30 years of tugging my 20 all over the state, every vehicle got
around 11-12 mpg towing ......
Thinking back
1988 Jeep Grand Wagoner 360 CI 8-MPG
(terrible handling 'cause of short wheel base)
1990 Dodge Ram Charger 318 CI 8-MPG (same as jeep short wheel base)
1993 3/4 Suburban 350 CI 12 MPG towing or not....
1994 3/4 4WD 350 CI Chevy 2500 P/U 11 MPG
1999 1/2 Dodge Ram 360 CI 11-12 MPG
2003 Dodge Durango 4.7L 11 MPG (actually tows well with short wheel base)
2016 3/4 4WD Dodge Ram Cummings Turbo (full delete) 23 MPG

Out of all of these my favorite was the 99 Dodge Ram !!
So long story short, good friend & I heading to Miami Dolphins game
in his new 1977 Olds Toronado with the 455, asked him what his MPG was?
Response was, if I found out it was 1/2 of what it should be what do you think I'am
going to do... Turn around and go BACK !
That has stuck with me ever since.