hesitation and rough idle.

i have a 2000 ford explorer 4.0 overhead valve. since i bought it it has always had a tiny shake, or hesitation. it has progressively gotten worse, the car will idle at 1 then goes up to 2 on its own then back down to almost stall or it does stall. it is better when it is in park. when the car is in drive the shake is much worse. we have replaced the o2 sensors, mass air flow meter, fuel injectors, Cats, and the problem has not improved. the exhaust still glows red hot and it smells rich like there is too much gas. the car cannot even be driven, it just stalls out no matter what we do. all the codes just point to o2 sensors or mass air flow meter, which we have replaced with new.