Car stalls while driving down road HELP!

This just happened to me on Sunday. Driving down the freeway at 2Krpm in OD and the motor just went slugish with no guts and stumbled to a halt. Would not restart. When it did restart it would idle at like 400 and choke. Waited a few minutes and it was ok. Did this 3 times in 20 miles until it finally would not keep running at all. Had her towed home. Got here off the sled truck, fired right up and pulled into the garage (like nothing was wrong). After about 5 minutes of running good, it started choking out and idled at 400 until it stopped. Re-started car, started fine then after about 40 seconds it dropped to 400 rpm's and choked to a a halt.

Sunday night pulled code 34 (EGR) out of her. Tps was at 0.85 VDC, FP at 36 (stock reg with vac on).

I replaced the 15 year onld EGR valve with a "spare" 10 year old valve that was cleaned up. NO issues with car. No codes KOEO

Monday, took here for a 20 mile trip and had no problems. However....

Found a cracked vacuum line (hear it leaking cracked) in the hose that goes to the smog pump valve (right next to the pump). And when under the car I found both cat-back pipes (at the H-pipe flanges ) was rotted through on both pipes. I could stick three fingers into each pipe!

I recently read a post from a stanger who had a surging idle. He recently replaced cat back with a different brand (or stock --I forget now) and his surging idle problem went away.

Is it possible that a major exhaust leak on the end of the H-pipe causes a back pressure issue that affects the o2 sensor readings? I have noticed recently I have an idle that swings about 200 rpm's (with the IAC unplugged and in closed loop mode). I suspect enrichment (or leaning out) from the computer based on o2 sensor input. What do you guys think. (plus the thermactor valve probably was not working....that would probably affect o2 readings? Right? )

PS I have gone through the car top-to-bottom for vac leaks. I am pulling 18 In/Hg at idle.

Did not mean to hijack post...maybe there is some useful info here?

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