The TOD uses electric clutches to pulse power to the front when needed. It won't lock in the front drive train continuouslly so it's OK on dry pavement. I'm not sure how the other full timers do it (probably clutches or viscous coupling). The TOD senses both wheel spin and engine torque when it decides to send power up front. So on your test drive, don't take it easy on the skinny pedal. I wouldn't worry too much about what the TOD lights mean ... just that there's activity on the display when you punch it.

BTW, the rear is posi so you'll get pretty good traction even if the front drive isn't working. I put locking hubs on mine & can't remember the last time I locked them.

BTW, if you're looking for the VX to be an economical DD to replace the Avalanche ... think again. You'll probably only get 15-17 mpg in it. I drive 100 miles a day so the VX stays at home on work days.