Eagle Fishelite 480 GPS

I'm sure most of you read my post a couple of weeks ago where my GPS unit quit working right. I kept getting an error message saying GPS unit not responding. This wasn't the first time but the second. I had already sent it back to Eagle for repair once before. I just got the unit back from Eagle yesterday for the second time. When I hooked the unit up to my boat a few minutes ago I find that the gps is bouncing all over the place. My boat is sitting still in my driveway and the GPS is bouncing over a 100' perimeter. What's so bad is this isn't even my original unit. Eagle sent my another unit that I'm guessing has been reconditioned. My question is is this a common problem with these units? I sure wished I could get my money back for this thing and invest that $400.00 in something different. I've always heard Eagle/Lowrance were alot better than Hummingbird and Garmin but now I'm not such a believer. I have replaced the antenna with a reconditioned one from Eagle and I have also switched from my trolling batteries to my starting batteries. Same problem. Hate to vent on you all but I'm just having to get this off my chest.

Had a go-round with Eagle back in the late 90's with one, globalnav.
Worked for 6 mo. or so fine, then took out - they worked on it, sent back
and it didn't make it one trip. I told them I was gonna start giving them
the kind of advertising they didn't want ;) and they sent me a comparable
Lowrance to replace it, it's still working.
But I think the field has leveled a lot lately, got Garmin and H'bird stuff now
too, and like it a lot.