RE: Off Road Park???
Mine was the Flowmaster 50 DeltaFlow, and I think there was another option for muffler brand. I've since gotten rid of the Flowmaster because it was too loud for my tastes on my 2.5L, it may be quieter and deeper on your 4.0L engine.
I'm running just a muffler-shop $20 turbo and may look for something closer to OEM to quiet this thing back down some more. I think mine may be even louder since I have no catalytic converter on there.