Where can I get a 3.5" cat delete pipe to bolt up to factory Exhaust?? Or can a get a regular cat delete pipe and is there a coupler?

You may have to get a 3 1/2" to 4" adapter, I have seen them for sale on the internet. 4" cat delete pipes are easy to find but I haven't seen any 3 1/2" pipes but someone will probably make one sooner or later.

You may have to get a 3 1/2" to 4" adapter, I have seen them for sale on the internet. 4" cat delete pipes are easy to find but I haven't seen any 3 1/2" pipes but someone will probably make one sooner or later.

If you could find one of these you could then get MBRP part number GMS9421 cat elimination pipe.

summit sells a dynomax down pipe thats 4" but necks down to 3.5 at the flange i think its like a hundred twenty bucks or something P/N 289-54194. I was going to put it on mine but found a local muffler shop that cut my cat out for fifty bucks.