Joined: Feb 2006
Location: Harrisonville, NJ
Losing the "punch" is from switching to the larger tube, you lost your exhaust gas velocity at low rpm. When the motor is at low rpm, the exhaust is not restrictive, rather it needs the smaller tube to maintain exhaust gas velocity. The motor still makes the power upstairs because it is pumping more EG and is less restircted with the larger tube. Its a trade off that everyone faces, low end torque or high end power. If you want to get your "punch" back go with the restictors, but you risk losing the power increase at higher rpm.
As for your loss in MPG, it is probably from lost exhaust efficiency at low rpm where you do your normal driving. The restrictors will help with that, but with some hp cost.
I think your best bet is to equip the motor to use the 2 1/2" pipes. If you don't already have it, but a CAI on it. It will help the motor intake more air, creating more exhaust, making the 2 1/2 pipes more efficient. It won't make a dramatic difference, but it will help.