Lewisville Muffler Shop, They put a FlowMaster on my Ram and did a great job.
Honestly I would see what they would charge for the cat as well. Most places will sell parts cheaper if they are also doing the labor.
Linky
If you want to supply your own parts then give Russ at Baertrax a call. He is in Dallas close to 35 and Royal. Of course he is out of town through Thursday this week. He may or may not be in the shop Friday. He will charge shop rate for the time. www.baertrax.com