When In Doubt, Always Shift...
Especially when you think the hill is too steep. Where do you live? The steepest street in San Francisco is a 43° incline between Hyde and Leavenworth.
Always shift down manually to a lower gear when climbing a steep incline, and use the same gear coming down the same incline...
As far as harm, the transmission should shift down for you when it needs the additional torque, so you are probably ok.
"We drive into the future using only our rearview mirror."
- Marshall McLuhan -
Northern California Wine Country...
"Turbos whistle, grapes wine..."