Learmech

I have a 2006 Chevy Tahoe I bought a couple of months ago with 155000 miles on the 5.3 vortec. It is obvious it has never been rebuilt as it burns some oil. I ended up putting some Lucas Oil engine oil stop leak in when I changed the oil this time. When I bought it the o2 sensors were shot. I replaced those and now I am getting a code for faulty cats. I am sure the blow by had killed them because who knows how long the engine has been burning oil. I need to replace the cats and might as well replace the whole exhaust system since this thing looks like it came from New England and played in salt all of the time. My question is what have you guys gone with as far as exhaust systems including cats and how hard is it to replace. I worked on Jeeps for years and they are easy not much experience with Chevy's that are twice as long. Any resources and help would be greatly appreciated. Yes I know I should have the engine rebuilt but I am a poor man with crap credit so band aids will have to do until I pay this thing off lol