This thread perfectly answered a question I've been considering since I've had some trouble dialing in my drivetrain based around a Deore RD-M592, a 9 speed Deore cassette, and a set of SL BS-77 bar end shifters. Glad to see that what I'm dealing with is probably mostly cable stretch and breaking things in, not incompatible drivetrain components.

Good luck, OP. Hope you sort out your setup.