Beemer I "did" have almost the same combo as you. (06 Dmax and 7000K trailer.)
I almost never turned it on unless I was in the mountains. It worked way too aggressive for that weight.
Depending on the terrain I would get better mileage with it off which makes sense because I was always adding fuel when going down hill. On the flats it did not seem to make any difference that I could tell.
Fast forward. Late last year I bought a heavy as lead Arctic Fox TT. I think it is 11 or 12K gross.
I tried to do the same thing............once. Never going to do that again! Now the procedure is get into the truck and put my seatbelt on and put tow/haul on EVERY SINGLE TIME! So as the saying goes, things change.
So if "I" were "you, with the setup you have right now" I would leave it off most of the time unless you are in the real steep stuff.