2011 Sierra Issues

[Wayne's GMC]

Hello, new to the forum. We have a 2011 GMC 1500 with 5.3 and auto trans. We inherited it after my father in law passed away, it's in great shape, 128000 miles...so the issue I am having first is some kind of voltage drop from 14 down to about 11.5, new battery, alternator tested good by 3 different testers, the low voltage seems to affect drivability with a sluggishness and slight hesitation, spark plugs were changed at 117000. Has anyone experienced this and what was the fix?

Second issue is a clunk sound when taking off from a stop light, I have raised the truck, in neutral, brakes released to check driveshaft and midship bearing, those seem good.

Any help would be appreciated, unless absolutely I'm not going to the dealer.
my email wayneyarian@yahoo.com
We live in Florida.

 

[98trck]

i have the same year truck
extended cab
while still under warranty i had the amp gauge acting up among other voltage gremlins
i explained it in detail at the dealer
the repair tech knew what it was ' there was too much resistance in the positive battery cable
he replaced the cable and i haven't had any more troubles
i have owned the truck since new

PETE

 

[Wayne's GMC]

i have the same year truck
extended cab
while still under warranty i had the amp gauge acting up among other voltage gremlins
i explained it in detail at the dealer
the repair tech knew what it was ' there was too much resistance in the positive battery cable
he replaced the cable and i haven't had any more troubles
i have owned the truck since new

PETE

Thanks for the advice, I will try to see what I can find out about it, was there a recall or campaign on the wiring? I can order a new wire from rock auto, but I need to see how long mine is. still not sure about clunk when starting from a stop.