Wideband UEGO Air/Fuel Sensor

I bought the one listed above for My 440 / 500 Stroker. I never set up a Holley before and it helped greatly as mentioned to see which direction I was taking things. It has since stopped working . If it was still alive I would have welded a bung and used it for tuning on my 340 Ragtop. Too much money for the short time I got out of it.
I still suspect a vacuum leak on my 340 since rebuild as it runs lean and I have to run half choked until really warmed up. I am soon the add a Air gap intake and then final tune carb. I have an AVS (originally on motor) and a Eddy 625 ABS (currently on motor) Thought carb needed rebuilding from sitting but ran the same so I rebuilt the Eddy and got the same results.