deciding between 4 or 5 inch exhaust

[bmoeller]

The decreased MPG is usually due to the increased pressure of the right foot while listening to the new noise.

[More Power]

The turbocharger is usually the biggest restriction in the exhaust system - for all non-DPF equipped trucks.

If I remember correctly, there was a proven power loss when a 5" exhaust system was installed in the middle-2000s Dodge Cummins trucks. To my knowledge, I don't know of a similar 5"/GM non-DPF connection.