Running Rich?

1989 LeSabre T Type
75k miles on Engine, 155k miles on Transmission (F79 gearing), 200k miles on the body.

I've had this problem for a while now and its driving me nuts. I'm only getting around 21-22 MPG highway. I know I should be getting more like 28.

Here is my current setup and parts I've replaced:

-No SES light or stored codes
-Fuel pump original to engine (75k miles)
-Swapped out different ECM's with no change (had correct PROM chips)
-New fuel pressure regulator
-Fuel filter has 20k miles on it
-Swapped in different MAF sensors with no change
-New IAC valve
-K&N cone filter on a FWI setup
-NTK O2 sensor about 10k miles
-Magnaflow high flow cat converter and Flowmaster muffler, about 20k miles
-NGK iridium spark plugs, Delco II ignition system, Napa Belden Wires

And here are my current symptoms:

-Strange Idle: It will be butter smooth and then it will jump a tad and then smooth out again. Seems to do it more when hot.
-Sulpher/rotten egg smell if I accelerate quickly

Here are my thoughts:

-Weak fuel pump. Could a weak pump not be supplying enough pressure to the injectors so that they are instead running rich to make up for the loss in pressure?
-Leaking EGR Valve. Letting gasses out of the engine to not re-burn for better economy. Would also explain the bad smell.
-Clogged/faulty cat converter. Explains bad smell.
-Overkill on spark plugs?
-Bad evap canister and/or purge solenoid (original to chassis with 200k miles)

Thats all I can think of right now but any thoughts would be appreciated. The bad fuel economy is really sucking my wallet dry and the fact that I haven't been able to find the source is driving me crazy. :runaround:

First scan it and look at what the o2 sensor is doing also look at fuel trims ( block learn), check fuel pressure, see if there is any sign of raw fuel in the oil. Just some issues that would explain a rich miture or the result of same.