The knock sensors allows the HO to run well on gas octanes from 87 to 93. The engine will produce more power from 92-93 octane because of advanced timing. With failed knock sensors, I'm sure that the computer defaults to the low octane mode whether high octane is used or not. The parts cost of the sensors is probably not very much, but the intake manifold has to be pulled in order to get to them, and the labor could be kind of high. I would check with a Jeep dealership on the price of knock sensor replacements before buying.
Both of them going bad would be a bit unusual. It could be that they came unplugged during some kind of service like a spark plug change and not plugged back together or repaired. Look near the rear passenger side of the intake manifold to see if any connectors are loose or dangling.
2001 WJ Limited with Quadra-Drive, Kenne Bell Supercharger, 3-inch Kolak exhaust, Stillen rotors (F/R) and MM pads, Addco sway bars (F/R).