It shifts into 4th under no load condition. Slightest load, it goes to 3rd and stays until gas peddle is released. For example when I have cruise set at 55mph it will shift to 4th for maybe 5 seconds until the vehicle slows a slight bit then back to 3rd to keep speed.

 

Throttle position switch "dirty" and giving ECU bad data, which makes tranny think load is changing? A live data scanner will show TPS%, it should be smooth, not changing rapidly all over the place. Clean contacts as a minimum.

 

At 55mph the throttle position is between 8.9 and 10% when in 4th. When it dumps itself into 3rd tps is 15-16%. Calculatef load in4th is about 24% and in3rd 32%. Dont know if these values are normal for disco.

Interesting note is that mass air flow volume is 0.0lbs. Perhaps the new mas is bad?

 

If gently shifts into 3rd and stays in third. Unless going downhill no load condition. As soon as throttle is pushed, back into 3rd is goes.