Pretty sure that truck has a computer-controlled transmission with little to no mechanical control over shifting. But still, start simple and change out the fluid. There's a great write-up on here about doing it by disconnecting the transmission cooler return line and running the truck while adding new fluid at the dipstick hole, but I can't remember who wrote it.

John B.

'87 Raider 2.6 Turbo Auto, Under Construction
'95 Montero SR, 35x12.5/15 BFG M/T KM-2's, Rock sliders, Qtr panel chop, gas tank lift, 2" BL, Aisins, 5.29s
'95 Pajero Mini
'98 Montero Winter Ed.
'04 Cadillac XLR
'03 Kawasaki ZRX1200R
'60 Ford Falcon 4Dr