You know you're boat better than me, so please take no offence. I checked the Grizzle at the Tracker page in teh boat desription it says it has "An aerated livewell in front of the console ensures that everything you catch stays healthy throughout your trip. "
Page for reference is
http://www.trackerboats.com/boat/?boat=3307.
You may want to check the live well real good and see if it has an overflow that is just restricted or clogged. In my boat, the aerator head is adjustable by screwing it in or out. If I open it all the way open, like you, my stuff overflows. But if I screw it in, it reduces the flow somewhat, then the overflow can keep up with it.
When I look at the side pisture of the boat at the bottom of the page, it seems to show a port. That might be the intake. In the photo section, the picture of the livewell seems to show the same aerator head I have, and something black behind it I take as the overflow.
Last bit, if its not an overflow, but....you do have a drain plug in teh bottom of the tank. You can create an overflow by finding a piece of pvc tube that will fit into the drain snuggly. Then cut it off so that its about 3 inches shorter than the total depth of the livewell. I had to do this on a boat I put a tank in, but didn't have an overflow and it worked just fine.