Hi brydy, A manometer can be bought for about $30 from Dwyer, and only requires a single hole to be installed in the flue pipe of the stove.
Is this auto shutdown still occuring?? It is possible the reset has gone bad, and is too sensitive... I'm not sure how to check it.
Is there a reostat controlling the draft from the power-vent system, or is there a flapper that is moved to make adjustments in the draft?
Can you just turn up the reostat a little to spin the motor a bit faster and increase the draft over the fire??
If this shutdown occured only when the wind was really howling, you may be chasing a once-a-season problem... pretty hard to verify that the problem is fixed... untill the wind howls again, just the right way...