I wouldn't try adding .005 to each side if it's already that tight. You will probably damage your shims if you try that. Maybe just try adding .005 to the right side to open up the backlash just a little.
I know that this is a little late, but if you decide to do another gear sometime don't get a Richmond installation kit, or a Ratech kit or anything else that Jeg's or Summit sell. The kits that DTS, Tom's Differentials and Randy's Ring & Pinion sell have the super shim sets in them. You can make much more accurate backlash adjustments with these, and they are much easier to use. The shims in the other kits are just not good enough.