Dragitup

I have followed the procedure to get transmission codes but the o/d light blinks continuously as opposed to pausing to give codes. Am I doing this correctly?
Neutral, O/D button in, jumper wire between TE1 and E1
turn key on (not to start)
O/D light then flashes continuously.
Any ideas?
The problem with the transmission is this-
Reverse works fine. No forward engagement in any gear until you put it in low and apply brakes and rev motor to @ 4000 rpm. Tranny engages with wheel spin and then works fine through low, second and drive shifting up and down automatically or manually. After you put it in park, neutral, or reverse you have to do the rev thing again.
Just flushed transmission with new screen. Fluid was dirty.
I have read mentions here about having to clean the valve body filters but haven't seen any instruction. Is there a tutorial I am missing?
Just bought the car with this problem as is so I don't have any history.
Car is 1994 LS400 with 161,000 miles. Thank you for your time.