Every year, as the venerable 4.0-liter six was improved, it seemed to lose power. By 2006, the reliable mill was working hard to move the TJ Wrangler. Rand fixed this by installing an Eaton supercharger with Unichip engine management. The horsepower was greatly improved while driveability was still at OE levels. In other words, there's no pinging and very little additional noise from under the hood. At the transfer case, a Tera ESS slip-yoke eliminator was installed.