Get a come-A-long and wrap a strap to the rear end then another to the muffler, take a grinder and make the slit's in the front were the U bolts are a little bit longer.
Back up, tighten up the come-a long and watch it hit the concrete.
i took the midpipe off with it, soaked it with pb blaster, stood on the midpipe and had my buddy hit it with a 5lb sledge.. worked like a charm! left some dents though.. haha
Remove U-bolts, cut slits in pipe, lube it up and smack the muffler by the inlet pipes with a sledge. It left some dents but I scrapped the stock system.
I unbolted the U bolts, sprayed a ton of wd 40 in between the pipes under the ubolts and started to work them around in a circular motion since the metal there has been compressed and formed. As they would get loose I'd spray a bit more wd in there and after a few mins it was able to slide off.