If you check the pcm history for codes you may find P0742 and possibly P1811 and unfortunately from what you have told me it sounds like the lockup clutch lining is coming apart and has created enough debris to plug up the filter. This is not a very common problem but it is common enough that it happens to a number of people. The valve body likely has some excessive wear and the torque converter lockup clutch has had extra slippage and created a lot of debris in the fluid and also in the valve body and solenoids which together made a bigger problem. You can try to do a filter/fluid service and it may help for a short while but the damage is done and you will likely need to consider a rebuild or replacement.
