25-pdvc/55shp 10 convection blower bogging down

My 9/09 Englander pellet stove's convection blower is not staying at set speed. It starts up fine but when the convection blower kicks in it runs fine for a while than it slows down than speeds up to the setting. Any ideas? Is it the motor or control board? Any more test I should? Help!!

When was the last time the conv. blower bearings were oiled?

I oil them quite often. At least twice a month. I half thought about pulling the motor apart and checking the bearings. Could this be the problem?

I'd just disconnect the power leads to the blower, and use a power test lead made of an old lamp cord and put direct 120v to the blower while it's still in the stove. If the rpm still wavers, then either the bearings are toast, or the power coming into the house isn't constant.

Oiling a motor twice a month sounds very excessive. You might have gummed the bearings up with too much oil.