Joined: Jun 2013
Posts: 4,094
Likes: 2
From: Bozeman
Bikes: 199? Landshark Roadshark, 198? Mondonico Diamond, 1987 Panasonic DX-5000, 1987 Bianchi Limited, Univega... Chrome..., 1989 Schwinn Woodlands, Motobecane USA Record, Raleigh Tokul 2
Good on you for climbing that hill.
In addition to the suggestions from Scott above, it could also be.
1. Wrong chain for bike (chain falls between gear.)
2. Worn chainrings.
3. Cross chaining.