I have been a member of the "Downshift club" in the past. Now note that each combo was within weight limits of tow vehicle.
Started with a Chevy S-10 and small popup. Worked well, the purchased a 21' Hybrid Keystone Cabana so that didn't work well as it would downshift in a slight headwind going DOWNHILL!
Moved on to a Dodge Durango R/T. Of course, you guessed it, bought a larger trailer, a 29' Surveyor Ultralite. Worked O.K. but downshifted constantly on any incline.
In 2009 found a great deal on a Ford F150 King Ranch. Pulled the old camper fine so of course we bought the 36' Laredo 303TG. More down shifting and white knuckles during crosswinds. I guess some of us are slow learners.
Found a great deal on the F250 diesel and couldn't be happier
W'ell be hanging on to this one for a while unless the lottery smiles upon me.
And there endeth the lesson. It's not just the weight of the unit that should enter the equation. The taller and longer the box behind the TV the more air resistance, both straight ahead and laterally during cross winds and disturbances from passing trucks/busses. So many factors enter into the differences between a 1/2 ton truck such as P rated tires, ride engineered suspension, frame flex, etc. and a 3/4 ton + trucks that are built to haul weight and tow. You will find adamant arguments from booth sides of this issue and I am just offering my opinion based upon my personal experience.
Let the arguments commence!