CRankin,
it COULD be your bike. I remember when I switched from Bike A to Bike B (I don't remember which now) I was stunned that suddenly it was EASY to stand up!!
and if you are doing 20% grades, you are NOT puny. I am not doing 20% grades. or even 15%.. maybe 11 or 12 sometimes. for a few feet... eeek.