Right, OK, I forgot about that. I should have remembered as my parents had a trooper for years.
This is for a 2001, should be the same:
Park the 2001 Isuzu Trooper on a level surface and engage the parking brake.
Slide under the 2001 Isuzu Trooper near the driver-side door. Locate the transmission pan on the bottom of the transmission. There are two plugs on the bottom of the transmission. The plug in the center of the pan is the drain plug. The plug in the recessed area near the back of the pan is the fill plug. You have to add transmission fluid to the recessed fill hole with the engine running.
Crank the 2001 Isuzu Trooper and let it run for about two minutes to heat up the transmission fluid. Crawl back under the Trooper and position the drip pan under the fill plug on the back of the transmission pan.
Loosen the fill plug with the 1/2-inch drive ratchet, extension and socket by turning the fill plug counterclockwise. Then pull the plug out and set it on the floor.
Pour transmission fluid into the handheld fluid pump. Slide the long plastic tube onto the end of the pump. Then insert the other end of the plastic tube into the recessed fill hole. Pump transmission fluid through the fill hole until the fluid starts to run out of the hole.
Pull the plastic tube out of the fill hole and screw the fill plug back in the hole. Tighten the fill plug back down tight with the ratchet, extension and socket. Pull the drip pan out from under the Trooper and turn the engine off.
Read more: How to Add Transmission Fluid to a 2001 Isuzu Trooper | eHow.com http://www.ehow.com/how_6698593_add-fluid-2001-isuzu-trooper.html#ixzz277WxQjF2