I have a 2001 that backfires

there is vital information missing here
to start with it is a v 6 so there will be 2--HO2S sensors one for each bank before the cat converter and 2 --O2ensors --one for each bank after the cat converter
there is a vast difference between HO2s and O2 sensors as each reports different information to the ECM
next slow acceleration can be accelerator position sensor or throttle position motor
every time you read the codes it cancels them so you have to run the vehicle for a few miles for codes to reappear
from the codes there can be up to 7 reasons for that code to appear so you don't pick on the first one as it could be another or a combination of others

maybe just a bit of un burnt fuel, if it has done it only once , common at high speed to leave unburnt fuel in cylinder when taking pressure of the accelerator

your statement that you disconnected the o2 sensor and all is fine tells you where the problem lies . It is in the o2 sensors . First up there are 2 different sensors in the system The one before the cat converter is a heated sensor (HO2S) while the one after the converter is only a O2S sensor . Two different sensors for two different applications and two different parameters that the ECM and CPU have to contend with. IF you did not use the correct tool to remove and replace the sensors then there is a distinct possibility that the wires have been damaged

Check for fuel supply problems as it sounds that at sustained high speed the fuel supply is not good enough. Possible pump dosen't have enough capacity

I guess the first thing I would check is fuel pressure.

Usually a sign of a miss-fire under load.
Common causes include spark plugs, coil, plug wires, injectors, or other things.
Is the check engine light on ?

Check for burnt intake/exhaust valves. Sounds like you have one or more not sealing correctly. Could possibly be a worn out distributor as well.

plug wires for sure are bad with it backfiring

I have the same car. So far no problems with the Transmision. I had the Trans oil change out every 60 K Sure sounds like you need to get the Transmision checked. Is the fault light on. I have invested ina fault code reader sure is worth it. 
Good luck.  Vilmos

if you don't have a gas cap on the car or if it is on too loosely then that is a possibility. Only other thing I could think of would be water in your fuel. You may try a bottle of "heat" (I think that is how you spell it) at your local auto parts store and chunk it in the gas can. if there were any problems with water that should be the cure.

Michael