Backpresure on 98 Rodeo

I just got a flowmaster on my 98 V6 rodeo. The shop actually sold me a one with the 3" inlet/outlet and used some couplings to get it to hook up with the 2.5". I want to eventually get 3" pipe from the cat-back. Was wondering if this would create any problems of not having enough backpressure on the engine? Any thoughts?

On a heavily computer controlled truck like this, the only difference you might notice is more exhaust noise. No *scientific* data to back this up, but the 1998+ 3.2/3.5 are pretty much maxed out HP wise, unless you modify them with a supercharger kit. The factory cat backs are pretty big as is, especially with the factory fuel tanker sized muffler.
G/luck
Joel