it was the spacer. added a spacer. having a bit of a time getting the limit screws set perfectly..Deore rd m5100 derailleur. I will keep fiddling with it. It was shifting perfect before so I know it is possible
. lining the low gear sprocket with the derailleur sprocket will sometimes cause the chain to over shift and other times not. if I tried backing off ie moving the derailleur slightly away from the spokes but then does not want to stay on the biggest cog. low speed I have the screw backed almost all the way out and the still not wanting to drop to the smallest cog every time. using a microshift 11speed bar end shifter and prior to adding the spacer was shifting perfect lighting fast up and down. I have the barrel adjuster all the way in, maybe I need to loosen the cable a little.