28 watts is totally wrong. If you're pulling 17mph up a decent hill, that should be around 300 watts, not 28.

Also, mine is a left only crank based model, so I don't know about the L/R balance stuff. You said you had the firmware updated, but can you do a "reset"? I don't pretend to know a lot about the "zero offset" and calibrating power meters, but I do know it is important, and if you don't do that, or do it incorrectly, you can get bogus numbers.