I have the 2160 (same machine, different motor), the "autogear" system. If it ends with "0" (2160) its a manual if it ends with a "5" (2165), it's the hydro. I looked closely at these things before buying one. I was worried about these trannies too! The transmission has an automatic clutch and 6 gears to choose from. Problem with these is that the pedal has to be FULLY DEPRESSED when driving to prevent premature wear of the clutches. The pedal is NOT an accelerator, it just engages the tranny.
After talking to my dealer he had a lot of horror stories of guys trying to mow in sixth gear and feathering the pedal which destroys the clutches. These transmissions are actually a lot more solid than the hydro and were designed for ground attachments...THEY ARE ABSOLUTE TANKS and rarely fail when properly used (when's the last time you rebuilt the tranny in your ATV? My 1980 Honda 110 and 1985 big red are still going strong /forums/images/graemlins/smile.gif).
I looked at the parts diagram and inquired about these things before buying. I was informed that they SHOULD last the life of the vehicle if used properly...IF NOT, no big deal, there are 4 (If I remember right) friction clutch discs in the rear end and they are only a few bucks each. Rebuilding is the problem, my dealer said it costs about 300 bucks (canadian) to rebuild the rear end...most of that is labour.
Adjusting the linkage would offer minimal improvement, the only reason it was designed the way it is is to prevent "jerkiness" when the tranny is engaged. I think they are usually factory set. Can't hurt to try though.
Bottom line, your clutches are probably burnt out and need to be replaced. Give your dealer a call, he may be cheaper than mine.
Good Luck
Taiser