1998 Jeep Cherokee Warm-up

Engine Performance problem
1998 Jeep Cherokee 6 cyl Two Wheel Drive Automatic 179k miles

3 minutes after warmup, car goes very lean, stumbles and can stall, you can "drive "thru it by stepping on the accell. A couple times. If it idles to long in cool weather (at a drive-thru) it will re-ocurr. Charge and temp sender match resistance.I've replace O2's w/bosch/denso and still get rear O2 code (wiring and conn. Good) run great once warm and 24 mpg