98 V6 Accord cat vs Ignition diagnosis? 300k

     Vehicle: 98 Acccord EXV6 non-CA emissions 300k. All stock. Last tune-up at approx 130k. Oem exhaust system still on car. In last 3-6 months have had "
insufficient EGR flow" DTC, a Bank 1 or Bank 2 O2 DTC, and a cat DTC code.. .I think. They come and go. Check engine light has come and gone, too. Rand omly I would reset the OBDII just to see what the recurrence rate was. Usua lly within 1-3 days the light would be on and one of the codes would be the re. - More importantly, suddenly last week in my morning drive I accelerated and it was as if the fuel was shut off....not low power, but NO acceleration/po wer episodes between 50-65mph. Hold my foot to the floor and it would event ually revive and lurch as power came back for 2-10 seconds and then repeat. Only way to get back up to 65-70mph was to "pulse" the accelerator with my foot for sporadic acceleration. Originally,no probs below 50mph (around to wn, let's say)...and if I could get it past 60 or 65 it would resume normal behavior. - Now, it seems the problem-range of mph's for this power-shut-down is expand ing above and below 50-65mph. Almost stalled once coming to a stop at an of f ramp. Have notice some marked stumbling, though randomly and short-lived, at idle. Now too dangerous to put on the highway. - I know tune-up is way past due...and cat is likely on it's 9th life, BUT ho w do I differentiate and keep my costs down while getting my normal/typical performance back. May have 2 culprits here contributing, but I could do a tune-up after the fact if the cat will get me out of the danger zone on the interstate. Help?
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