92 Explorer running rich Help please

the explorer will idle warm but will shut off after a few seconds cold ( it will sometimes shut off before i can get under the hood to the throttle cable) It sounds like it has a miss in it but cannot identify by pulling plug wires. miss is more pronounced with higher RPMs. even worse with a load (in Drive with brake on reving engine) engine code only signals code 173 (o2 sensor indicateing rich) Like I couldnt tell by the exhoust smell.
All wiring harnesses and vac. lines seem to be connected.
I have checked and replaced just about all I know to.
new O-2 sensor
new bosch plugs then new autolite plugs (gapped right)
cleaned MAF (have 2 used cleaned and tried both)
new IAC
new air filter
new TPS
new CKPS (crankshaft position sensor)
new ignition box

I am thinking it may be a timing issue (belt slipped ?) is this possible?
Haynes manual requires engine removal to remove belt is this known to be true?
or the powertrain control module?
or the ignition control module? Also the tach registers 3000 RPM at idle
and 4000 with a little throttle, with the key off the needle drops down as usual. Im not sure how it works exactly but seems like it may be a clue.

any suggestions?

What engine do you have? Have you checked for excessive fuel pressure? (Normal= 35-40 closed throttle, 50-60 when snapped open or referance vac line disconnected from regulater.) Have you checked for leaking fuel injecters? (rapid loss of pressure after key turned off.) Fuel pressure regulater diaphram rupture (fuel comeing out of the vaccuum port) Idles at 3000 rpm! Are you sure the TPS is set correctly? And are you sure the MAF sensors are calibrated for your application? What came first the chicken or the egg? Can you give me a timeline of concerns and "repairs" to work with?Just some thoughts to start on! Let me know what you find!