i've been around here since '01 and own a '99.

first off, yes, these engines run rich and that's why the O2 sensors, pre-cats, and main cat go bad prematurely. that said, there are plenty of 2.5 and 3.0 engines around for the taking. they cost about the same, honestly. if you just want the pre-cats, i see people auction them off after buying headers.

i recommend buying MIL eliminators, gutting the pre-cats, giving the intake and fuel delivery a cleaning, and see if things improve. if you want more power or confidence in the car, then upgrade to a 3.0 block.

1999 Cougar V6 MTX Borla stainless, dual exhuast ST200 struts, rear strut tower brace Roush springs, rear sway bar, bodykit Steeda Tri/X, Powerslot rotors, Falken Ziex 512 Awaiting install: GMK CAI