1870 is componet slipping and is generally only set when lockup is comanded in third or fourth gears and the expected engine to output rpm is significantly off , Usually its TCC slipping code . I would suggest calling around trans shops for one who has a schafer shifter , Its box that plugs directly into the trans and allows manual control of all solenoids with PCM disconnected if you can get everything to work with it you are dealing with a control issue tunng etc,

 

What did you find out ?