Towing a Casita

then what is struggling depends upon ones view! 50 mph at 5000 r's is struggling for some, when that is what and how the engine was designed to tow said load up a hill. My dmax to me is struggling at 2800 rpms when moving 25K gcwr up a 4% grade in 3rd at 40-45 or so! If the chassis is able to handle the trailer, a lower HP rig will go slower than the same chassis higher hp or bigger motor. Hence why some manufactures, MB is this way with there SUV's, you can have a 3.2L V6 gas, it is rated to 5000 or 7500 depending upon the year ML series suv, as the turbo diesel or the literally supercharged 5.5L V8 with double the HP and torque numbers. The owners manual states, for better performance, get the larger engine. Otherwise, you are safe towing with ANY of the motors!

Marty