If the joy stick you refer is the lock out up (disengaged pilot controls) it provides a little more flow for the drive motors.
But I dont think that's the main issue, as spanner say check the little things first, Hyd level, filters, suction filter etc.
Then raise it off the ground and cycle both tracks - they should run the same speed. Then try each one touching the ground to see if one is weak, or put your bucket and blade down and try to run the tracks.
Last, your drive motor(s) may be getting weak, 3-4000 hours or so is typical life depending on conditions, fluid changes, drive maintenance etc.