[jamesrr]

Rob
I feel your pain, My "burb" has also stumped me.(See 88 bucking)
Your problem seems to be in need of basic rethinking. I'm not one to just throw parts in and see what happens next.
Look, one thing burbs have a reputation for is power
and if yours has low hp begin at the basics
air in fuel in exaust out timing/compression
when you went to aftermarket exaust did you change the cat?? a exaust restriction could be the problem.
If it was me I would disconnect and give it a test run.
How many miles?? I'm wondering about compression.
compression gauges are cheap or can be "borrowed from auto parts stores"
Did you actually test the fuel pressure?
This is also another gauge that can be borrowed
not purchased.
Good luck. let us know