The hill was on the NJ side, west of Pennington, maybe Poor Farm Rd. (see njbikemap.com, Pennington area map). I figured out later that I probably had a slowish leak from the start, which caused me to struggle on the hill - it wasn't a terrible hill or anything, but flat tires do make them a little tougher.
I did then go down Pleasant Valley Rd., to Rt. 29 along the river, and south to Church Rd., out of the valley. No really significant climbs.