06 Crew cab custom exhaust

[jesus8005]

I been recording my mpg and all I get is around 14.5 in Houston. I wanted to up to do a custom exhaust with pacesetter long tubes 70-2265.
Custom y pipe two 3" inlet and a 3.5" outlet. A MagnaFlow 59920 - Universal Spun Catalytic Converter.The muffler will be a MagnaFlow 12587.
I will want in exit before the rear tire. What do yall think .....what tune should I get........I heard you have to tune the truck when you put long tubes beacuse you have to remove two of the O2 sensors

[1988 GMC 355]

2.5" y pipe will be better, 3.5" is to big for an outlet, you want 3", the stock cats are high flow so no need to get new ones unless you want to, that sounds like a great setup, just don't dump it or it will drone bad.

A tune is only needed to tune out the rears so you don't get a SES light, Blackbear, Nelson, PCMforless are all ones people like on here.