2006 Duramax diesel GMC Sierra 35000. 6.6L. Question: no hi end power hard starting power drainage sometimes over night.
Answer: Hard to pinpoint an exact problem without a little more detail, but it seems like you might have a couple different issues going on. With the hard starting and no high end power, you could have something as simple as a clogged fuel filter, or air filter. You could also
be losing fuel pressure or even have gotten some bad diesel fuel. If there is a check engine light on, any codes stored would help in finding the problem. As for the power drainage overnight, you could have an excessive draw on the battery that is killing it. Any aftermarket accessories would be first to look at, such as alarms, remote starters, lights or trailer wiring, etc. Or it could just be a faulty battery.
GMC Voltage Fluctuates
2000 GMC Sierra Engine Size : v6. Question: voltage fluctuates and the battery light flashes on my 2002 GMC Sierra.
Answer: Usually that means you have a faulty alternator when you see the battery light come on while the vehicle is running. I would get both the battery and alternator tested on your truck. If the alternator has not been charging sufficiently, then the battery has been taking up the slack, so it may be on the edge of being bad as well. If neither test bad, then you might want to check wiring to the alternator, and PCM.