Sorry to burst your bubble, but there is no way a drill powered dolly will push or pull your 6500+/- lb 22' AS up a grade, let alone what will you do to power the brakes on the trailer to keep it from rolling away from you, or over you!
BTW - the powered dolly makers do recco always pushing the trailer up, & pulling down - with the dolly downhill so the tongue weight is on the dolly for it's tires to get traction.
In this situation small is not helpful.
Eventually you'll need to get a real dolly with a 1/2 HP or so electric motor, & there are several mfgrs out there whom you can check out.
I got the Power Mover, which is custom made for each customers needs from their range of AC & DC powered dollies, & they can make it with a brake control for the trailer's brakes on a grade.
I have a 3000 lb (wet & loaded) 1960
Avion T20 vintage kin silver twinkie, & an 8% grade at the front of the driveway for about 20' & got the 1/2HP AC with brake control, onboard 12V
battery to run the brakes off the 7-pin connector & 5 wheels (3 or 4 would've worked for the pavement, but I also need it on turf in the back yard to the ultimate parking spot).
Get the weight of your trailer(wet & loaded) , length & % of your grade(s), then call & talk to Brady there.
Check out the others out there too.