Electrical issues?

[sierradenali920]

Hi, I own a 2003 GMC Sierra Denali. The other day I noticed that none of my gauges were working while I was driving. I stopped over at a friend's house and shut the truck off. When I tried to start it, my battery was dead so I got a jump. I haven't replaced the battery for a few years so I thought nothing of it and just replaced the battery. I thought that would've fixed it but as I drove it with the new battery, my lights would dim and the truck would lose power and shut off. I put the truck in park and restarted it and it started and drove home. My battery light kept coming on so I then replaced the alternator. Even with a new battery and alternator, I'm still having issues. My lights dim when I use any electrical components but get bright when I accelerate. When I slow down or come to a stop it seems like the truck is about to die and my battery gauge drops. My battery gauge fluctuates a lot and some of my marker lamps flicker. Any tips pointing me in the right direction would be appreciated. Thanks.

[8.1HD/ALLISON]

I would start by checking and cleaning the battery connections, and grounds. Sounds like it could be a bad connection.