Flooding bad is the only reason for gas in the exhaust - or maybe warped exhaust valves.
A plugged precat is a plugged cat, and gas in the exhaust is really bad for the cats.
What year/engine/milage we talkin? and how long has it run bad?
Forget the EGR right now and find out if the precats are plugged (there was even a recall on some) and then find out if it's running rich. Then the EGR.
Backpressure is measured with a low pressure guage connected to the upper O2 sensor holes, or the back can be checked by hooking to the upstream DPFE port on the EGR tube.
This tube goes back between the engine and firewall and hooks to the exhaust manifold. I use 3/16 rubber hose and a vacuum/fuel pressure guage. Over 3psi aint good (while revving).
