Change the electronics in the trans. Sensor return values changed in 00. Having sensor/model year mismatch gives you exactly the symptoms you describe. So, buy the sensors/solenoids for a 99, grab the retainer you will need out of the old transmission, (governor pressure sensor retainer I believe) and swap 'em out. You can get complete sets of them off ebay for around 200 bucks. (governor pressure sensor/solenoid, o/d and tcc solenoids, even an output speed sensor. most come with filter and gasket as well.) Make sure it comes with the borg-warner heavy duty governor solenoid. Adjust the bands while you are in there.

 

I was in a time crunch so I removed the trans harness and big black plug from the trans,by dropping the valve body down and swapping all the older electronics, temp sensor, governor sensor , the solenoids were the same but still swapped them out works perfect.