I bought a 98 Disco last week and so far I'm loving it! 71k miles on it and most everything is in working order.

I did notice something strange that may be normal but when I’m traveling at highway speeds (65-75 mph) and I push down the accelerator all the way to pass the transmission does not drop down a gear. It does drop if I’m at a lower gear and try to pass but not at the highest gear.

Some pics can be found here –

Oxford Blue Disco

 

You may be just outside the rpm shifting range and the ECU is not allowing the down shift. How long has it been since the tranny was serviced?
Mike

 

I dont know the past history (I know thats bad) so I cant say when it was done.