Clock resets to midnight? 2004 Sierra 1500

[bandjw01]

I have a 2004 Sierra 1500 SLT 4x4 5.3 v8 with 63,000 miles. I am retired and don't put many miles on it. The clock is correct when I turn on the key but when I start the engine the clock resets to 12:00AM. According to the ammeter, the system is charging. Battery is about 3 years old. Battery cables are tight and not corroded.
My first thought was the battery was going bad, not holding a charge? I put a battery tender on it for a few days, fully charged, still the clock resets to midnight.
How do I fix this?
Thanks,
Bob

 

[Parts007]

I haven't been able to figure this out, but are there two power sources to the radio, like on the older vehicles? One source is batt power, one source is ign power.. Just a thought.

 

[ktownloudog]

Sounds like a ground issue somewhere. Maybe for the PCM. Or possibly even an internal short in the PCM. Definitely a KAM (keep alive memory) issue.

Have you checked the ground connection for the battery where it bolts to the body? Maybe its dirty.