[Mihir Juvvadi]

Its been said by more than a few others, but I am almost positive your problem is simply low pneumatic pressure to your shifting actuators.

The clicking noise you described comes when the shifting shaft is not in full engagement into one or the other gears, and the balls interact with the contours in the gears.

In addition, this diagnosis would cause the jitteriness you described when driving. If the shifting actuator is not getting its full pressure (60 psi), then the shifting cluster could easily start to disengage.

Check pressure regs etc. on the bot, and it should help.