now, THAT could be your problem. yes, the groove could be worn out from using the larger wire w/ the smaller groove. you shouldn't have to change the drive roller pressure at all for switching to a smaller wire size. i'm betting that's what's wrong...find a new drive roller for your machine. and no, .001 isn't enough of a difference to matter on a drive roller. i use .023 or .024 contact tips, and never notice a feeding problem.