1995 850GLT poor shifting/acceleration after exhaust/O2 sensor replacement

[Alan99]

Hello all,
I've had this vehicle 5 years or so with no questionable issues, currently about 230k. a few months ago I replaced the muffler and cat. When removing old cat the upstream O2 was froze in and stripped leaving no choice but to let it go with old cat and get a new sensor. The new cat was not designed with a downstream bung,so at the time i left the downstream wired and not installed into the exhaust. so at this point the car was driven for about a week in that state which is when poor acceleration and refusal to shift into higher gear once reaching about 40mph or so and would top out about 55 mph and burned more fuel as expected. I attributed that behavior to the lack of upstream and figured when i get the new one in it will straighten out during the readiness cycle. new sensor in, no change. purchased a collar style bung and installed the downstream. no change. disconnected battery for about 15 minutes to clear computer and restart readiness and driving behavior. no change.
when accelerating beyond the 55 area it will speed up extremely slowly while the rpms shoot up near 4k while still not shifting into high gear. when circumstances are right it will struggle up to 65 mph. none of these issues were present before initially disconnecting the upstream O2 sensor. it has also been sporadically dying for no apparent reason and will always start right back up almost immediately. The only code i'm pulling is P0108 for the MAF/VAF circuit which has been there since i've owned the car. any insight on correcting this would be greatly appreciated. I preemptively thank you all for your suggestions.