Rich means too much fuel but it can also mean misfires. When referring to the smell do you mean a raw gasoline smell or an acrid smell coming from the tailpipe?
The fuel pressure is too low and I wondering if this low pressure is causing such a problem with the injector spray pattern and which in turn can affect mileage, performance, and so on.
When, if ever, was the last time the fuel filter got replaced? In the auto engineers infinite wisdom they put the filter inside the left front fender on the LS; out of sight and out of mind. The wheel must be removed along with the inner fender to access the filter.
If the filter is clogged it's also quite possible for this to weaken and eventually kill the fuel pump.
The codes you were given point to an O2 and catalyst but this is unlikely to have anything to do with the problem with one exception. That would be if the converter is clogged to some degree. A clogged cat can cause poor mileage, acrid exhaust smell, lack of performance, etc. This could be checked with a vacuum gauge.
I have no idea why the fuel pressure issue hasn't been addressed and hope some of this helps in some way.