Air/Fuel sensor

I have a AEM in my big block.I used it for tuning my Holley 850. I never did it befoere but was a great learning experience. Carb works great. 13.2 at idle 13.5 cruising 12.2 ish WOT. Now it's stuck at 14.7 all the time . Only got a couple of years out of it. Still haven't fixed it yet. Now I want to Dial in my 340 Ragtop and want to try a different brand.