unless the larger tires are lighter... you travel more distance with fewer turns of the driveshaft = lower RPM needed to maintain speed

 

On my 2003 2door Blazer I added the following:

K&N FIPK
Gibson Catback exhaust

I personally have noticed throttle response is much faster. It also has a nice exhaust tone now. So for under about $600 I believe it was worth it.