I87 through New York, into Montreal...How steep?

The Rockies are mountains. The Grand Tetons are mountains. The Adirondacks are giant hills. You should have no problem. I wish our Adirondacks were taller and more majestic but they are lovely and have lots of lakes and streams all around. If you plan to stop in the ADKs be sure you have a generator. None of the DEC or State parks have hook-ups- not even electric.

Not much worse then running I-81 thru Pa. I-87 runs up basically the east side of the Adirondack Mountains.

I-87 does have some hills that drop our coach out of overdrive for awhile in the northern section, but they're not that long for the most part. I-40 and I-26 going into Asheville from TN both have more impressive climbs as I recall.