I have a 2001 Montero sport XL3.5 and it seems to have a pretty erratic shift. Tough to describe but it seems confused on which gear it needs to be in and when it finally picks one ( mostly 4th it seems ) it almost
" hesitates " before locking in. in the lower gears it seems to want to think about which gear it goes into. I did do the 4 quart oil change with the sp III specified oil which did not seem to make too much of a difference. I plan to change the ATF again with the next oil change but it just seems a little concerning. As a side note the old oil was a little dirty, no foul smells, and the car has 113,000 miles on it.

Any info would be appreciated, Thanks, Mike

 

have u try flushing the ATF?
if that still does not work,the gearbox solenoid valve needs to be change.
common problem on auto gearbox when the fluid gets dirty.
only way to know for sure is to check it with thatelectronicdiagnose thing.