Also check water bypass hose off upper rad hose connection. I'd stop driving it until you get this figured out. Not sure if this is relevant but thermostat needs to installed at certain angle. I'd also try to inspect cavity under intake for coolant where the water pipe to the runs into the rear of the water pump. Taste the water coming from tailpipe for sweetness.

92 Montero LS 3.0L V6 Auto, Stock, Original owner, 185,800K miles