The other day my A/T light started flashing and it took about 3000 RPM to get Montero to move. When I stopped on a hill in drive it felt like a brake was sticking, After checking all wheel brakes, all fluids It rolls easy when pushed in neutral and will roll easy in low gear with engine running. But when I put In Drive it is like the engine is fighting a brake. How does the "Hold" mode work? could it be the issue?

 

You need to scan for codes if your Montero is a 96 model. Otherwise, I'm not sure how you would deduce what is causing this issue. Hold keeps the car in 3rd gear to make it easier to launch in wintery conditions. This would not influence higher speed driving. Also, your hold light would be on (if not broken). Push the switch and see if it changes anything?