My heat is 'warm-ish' instead of hot. The airflow seems pretty weak as well. The blower motor does run on all speeds, but it is noisy...makes kind of a rumbling sound. But the weirdest thing is that the vents in the center dash disagree. The left one blows warm-ish and the right one blows cold. Both outer side vents are warm-ish. I plan to pull out the blower motor and look for crud and broken fan blades first. Not really inclined to blame the heater core yet. Any ideas on my disagreeing center vents?

98 Montero, 184k.