Lokar Guage insert - 6 Guage?
http://www.lokar.com/product-pgs/interior-access/interior-access-pgs/interior-access-pn.html
Need 4.6L Tuner/Programer
Spectre (guy@spec)
Recommends SCT or HP. He said look at the PID (Paramter ID) and the "long term fuel trim". Should be +/- .03 (by 0.0 to 0.3)