6 and 48 are good, I think that is what i have mine set at.
make sure you have the stoker motor bolted tight to the bottom and it's not uneven.
Maybe the stoker wheel is slipping or something is jamming the plate. drop the stoker motor down and check the Rotating Wheel, sometime if you try and push the plate back and forth it can loosen the stoker wheel, I believe it is a backwards thread. Mine came loose once and lost the fire on the one side, couldn't figure out what happen until I dropped the stoker motor and the rod/wheel had fallen off....
I know some of the newers CoalTrol only ones, they eliminate the stoker adjustment screws....mine was converted from Rheostats, so I still have the adjustment screws, but both I think are screwed all the way in for Max. FEED Adjustment. I let the coaltrol maintain it.