ADAIR TRACKS, WITHOUT 'EM YOUR JUST SPINNING YOUR WHEELS
REMEMBER KIDS, THE FIRST "A" in AATV STANDS FOR AMPHIBIOUS
My tracked 2007 max iv has the 27 hp motor with 12 tooth sprockets on the t-20, pulls like a champ and i really like the lower gear it gives. It uses a bit more fuel than i'd like if you are on smooth terrain and (going to and from a location) in the upper rpm of the range. However, crawling around at lower speeds dont seem to show much ofdfference in fuel use. So, short distance isnt an issue but if you do the 12 tooth swap and plan on long distance driving you may consider bringing a few extra gallons of fuel than normal.
The How to Rebuild Skid Steer T20 Transmission article shows you all of the steps to pull apart the T20 which is pretty simple. The more involved part may be replacing the sprockets on the output shafts. Your sprockets may just be pressed on or they can be tack welded as well (removing welded sprocket). Once they are off, you can press the new sprockets on but you may need to freeze the shaft and heat the sprocket before hand to get everything together.