I used to pull a 18 foot work boat up a fairly steep ramp with my old diesel rabbit. Boat, motor, trailer probably topped 2000 lb. It was hard on the clutch to pull it up (love that smell!!), or the wet tires spun. So we came up with a novel approach.
I would get boat on the trailer and pull it partially out. Put strap on boat so it was firmly secured to trailer. Then a helper (necessary) jumped in the boat and got behind the console. I would back the whole rig down til back tires were getting wet (but not brakes). The trailer would float under the boat, attached. Helper fired up outboard and trimmed it partially up. He would put it in gear and give it a few revs. When I beeped the horn he firewalled it, I let out the clutch and hit the accelerator. When the prop caught air, he shut it down. By then I had enough inertia to finish the climb up the ramp. People at the ramp actually cheered.
The rest of the tow was just on neighborhood streets so handling and braking were not too unsafe.
I had to know how high to trim the motor to keep the skeg from hitting ground. The first time we got it wrong. Second time on, no problem.
-Eric