all u got to do to see if its partially clogged is unscrew the o2 sensors to give a place for the exhaust to escape, and if it is a clogged one your truck will run 5 times better

 

Pre-cat or post-cat?

 

ide do front ones first than back

 

if you are thinking of getting rid of your cats do like i did i ran a quarter inch drill bit up through the center of them and tapped them with a hammer and man the s@#t that came out was unreal but made a big difference on how my truck runs

 

I think I will do that. It should be involved in tune ups IMO. I had a buddy that would cut the cat(s) out and ram a pipe through them and then weld them back up if I remember correctly.