vx commodore losses power and speedo stops working

I had a similar problem one day when driving my entire instrument panel died and I had no wipers but it righted itself. Couple of days later on the way to work engine and airbag light came on, then lost my speedo and gauges, I turned home but very slowly lost power till it died on the side of the road, lost power steering brake booster...basically everything. I removed the alternator and replaced the regulator on it and that fixed it. The reg stops over charge and negates all unwanted power so without it you go through a cycle of over charge. Hope that's all it is for you, new reg is bout $60

 

Sounds like your VSS (vehicle speed sensor) is intermittently faulty or some other electrical problem is causing your transmission to go into limp mode (you will only have third gear and second if you select it manually).