Re: 2001 6.2 alam
sounds like the engine is throwing a code, and the resulting in the engine being put in "guardian mode" which reduces power to protect the engine. The quickest and fastest solution to this problem is to have the engine hooked up to a laptop or a mercruiser scan tool. I know that's not what you want to hear, but it will get you back in shape the fastest. There are many sensors that will put the engine in to guardian mode.. block pressure sensor, oil pressure, temperature sender, throttle position sensor, crankshaft position sensor....the list and various combination's will have you pulling wires and guessing for a long time.
Also, since you mentioned voltage, those engines require a lot more voltage to run properly, and they are very sensitive.
Bottom line here is, your engine computer has a code in it, find out what it is.
PS. If you don't have smartcraft gauges, your engine will automatically have all of those codes stored inside them. I think its 5 total, maybe 6. I don't remember. Just ignore those.