Does your A/T light stay on or blink intermittently. if it stays on it is due to overheating of the fluid or overall transmission temp. if it blinks it is due to an electrical issue like a faulty speed sensor. this applies to my monty it may not apply to yours.

if its overheating best bet is full flush including secondary cooler and if it doesn't have one consider getting one.

95 Montero SR - center/rear locker, Modified 6G74(200rwhp),Stock suspension, white with gloss black trim!

07 FJ Cruiser - rear locker, all stock!