Ramp- I had the same thing happen on my '02 Duramax. Don't know if it will help or not but you might take a look. The battery cable on the passenger side was corroded on the inside where you could not see it. Take it off and remove the center part and give it a good cleaning in baking soda. Use a wire brush to clean the posts, etc. I bought new batteries thinking that was the problem. Of course, at 5 years, you are probably on borrowed time for the batteries. This has been two years ago and I am still runnning the OEM in my boat.
'99 25' Safari
2 Honda 2000i generators
'08 Chevy Duramax
'01 Yamaha Raptor ATV
'07 Yamaha Rhino ATV
2 burgler alarms: Rotweiller and Shepherd
"If you step down to get in, you have to step up to get out"