Jack up the Jeep and let the axle hang down as far as it will..... gaining clearance between the under tub and axle. Another problem is Jeeps that have trailer hitches....like mine, The exhaust tip hit the hitch. My case, I cut the stainless tip off and installed a rolled down tip ...looks good and works great.
Make sure you have the exhaust inlet / out correct...I forget as of this post, however I believe when I installed mine the muffler has the in let outlet off center from top to bottom. I'll look today and post back unless someone here knows for sure.