echo dave
you got an electrical issue
you should have more than 13.1 volts running even at 2500
drop into autozone or one of them places and let em do the half baked load test it will help isolate teh issue
whether you got a shorted cell in the battery or the alt is going south, loose connections, bad ground, etc
11 volts at rest indicates a load.
overspeed the engine..... only can solve that?
hope we helped some