Your charging voltage sounds fine. 13.6V+ when hot, 14+ when cold. It can be a bit lower at idle if you have lots of stuff turned on (headlights, brake lights, interior fan, etc.).

Shift points are handled using shaft speed sensors in the transmission, not the speedo signal that is routed through the gauge cluster. It has to do this due to the 2-speed transfer case. The gauge cluster speed signal comes from the ABS module (wheel speed sensors), that then routes it to the ECU. Tach signal comes from the ECU to the gauge cluster.

By factory test mode, I mean for the factory that made the gauge cluster. So, Toyota wouldn't even know how to set/use/adjust. It would be used for setting the needles in the correct location during assembly, probably. No way to prove that though.

At this age you don't legally need to have the correct mileage on the odometer. I bet there is a service out there that can do it though. You might also be able to swap your speedo/odo module into an otherwise working cluster. I don't know where the mileage is stored on the cluster though...

-Charlie