I am having a problem that has gotten worse over time. It takes a long time to get to top gear on the highway. Now it wont go in to OD until the vehicle has been on the road for 45 minutes or so. When it finally does shift to top gear, the OD light switch on the dash works. I can turn OD on and off - the tranny shifts up, then back down like it should. Any ideas of what might cause this?

1991 LWB Montero LS 213kmi - original. Stock.
2003 LWB Montero LTD 95kmi - original. All leather, stock and sweet

----Drive it like you have to use it to get to work in the morning.----