[JessR]

We have used a 2 speed tranny with encoder driven autoshifting the past 2 years and find it works well. As with Sparx above, we have offset the upshift & downshift points. We also reduce power for the 1/4 second or so it takes to shift.
Similarly our (homemade) 2 channel encoders give a quadrature signal that lets the software keep an absolute count & if you're going forwards or backwards.
Note in software you can 'have it all":
A toggle switch on the driver controls is labeled 'auto - manual'
In manual mode the trigger upshifts & thumb button downshifts.

With velocity based shifting, autoshift is just the thing for those closing seconds when you are distracted, burnt out & need to just peg the joysticks and head for home.