My synchro shuttle sometimes used to growl at me if I didn't come to a complete stop before throwing the reverser lever. Now I'm in the habbit of stomping on the brake as I reach for the lever. No more growling/grinding, just happy tractor.
Yes, I have tried that as well. Even when I am stopped, sometimes it grinds a little into forward. Reverse, never. It never used to do that. I am hoping there is an adjustment or fix without digging into things too deeply, but not sure.
The only adjustments I've ever seen on a 6000 are linkage related. there are some links and toggles under the sheet metal panel below the steering wheel. You might check them if the lever travel feels restricted or does not fully engage the shuttle, but if the synchronizer simply feels rough and/or hard to engage, I doubt that any adjustment will cure it. Once you get it locked in, does it perform OK in forward, or does it ever fail to drive and cause you to shift back to neutral and try again? Has it ever jumped out of forward while traveling?
If it's not jumping out of gear, and the lever travel feels like the distances are about the same as always, I believe you're resigned to live with it this way unless it gets worse. Should you decide at some point to replace the syncronizer, I suggest you research the process before attempting it on you own. I replaced that same part in a 6000 last spring, believe me, there are a lot of parts on the floor before the syncro is out and on the table.