With Max, I didn't do the increment thing, so it sounds like you will have a much more successful approach
When loading into the back of the car, here are a few of my observations....
Max has a great tendency to try to fake me out. He might go half-way up the ramp, but then will try to either jump off the ramp, or jump the rest of the way. (hhhhmmmm, same problem when Indy was learning agility way back when - bet agility trainers are good with this).
I have to make sure that I keep a short leash on him, and I think I even hold his collar to quide him so that he doesn't try to jump it midway (careful for the fake!!)
Sufficient speed is required to go up the ramp initially, if they are not used to hills or climbing. I wish I would have gotten the one with rubber, I think it would have been better, I have the one that is kinda like sandpaper at the bottom, I didn't realize it when I sent away for it, I goofed.
Too little speed gives him time to think about jumping off. I don't know if it makes it more difficult to climb too.
When I first introduced it, I tapped it, named in "ramp" (how obvious, eh?), and we had to start about 3-4 feet back to get him properly lined up, he wouldn't go up it straight if he was too close to it.
Coming down, again, I have to grab him at the collar to guide him, so he doesn't try to jump mid-way.
He knows the words "ramp" and "step", so I do use those, going up, and coming down.
I haven't used it in awhile, since Max is on super restricted activity, so I may be forgetting some things.
My strongest word of advice? If you are not used to lifting out a 75 lb dog from the back of your car, it's best not to start now, I speak from experience