'92 Grand Prix running too rich.

I had a stalling problem on my 1992 Grand Prix LE (V6 3.1L) which was fixed by changing the ignition module (used one but kept my old
coils). Ever since, the car is running extremely rich in fuel.
Prior to the stalling problem, it used to do on average 425 km (264 miles) on a 60L (15.85 gal) fuel tank, however, it now only does 280 km (174 miles). It also has an hesitation when i give it gas from a standstill position (or even a slow roll). That problem also started after the stalling repairs and may or may not be linked to the same problem.
I've had two mechanics look at it and they can't find anything apparent. Any clues, guys?
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