I see in your profile that you have a '95 Montero SR. I'm not familiar with the transmission in the '95 - but a word about the earlier models:

I recently bought a rebuilt torque converter for a '91 A/T which has a lockup torque converter. The installation instructions included a caution to replace the torque converter bolts with new ones since the bolts stretch when torqued. In the earlier KM148 non-lockup versions the bolt stretch may or may not not be an issue, but the lack of internal clearance in the lockup version definitely causes torque converter damage. DougB and I have measured the length of a new torque converter bolt and compared it to a used bolt. We both found the caution wrt to bolt stretch to be correct. I'm not sure the bolt issue applies to your torque converter.... nor am I sure if it applies to OE converters that have not been remanufactured.

All that said, I don't think your problem is in the transmission. Since the vibration is evident in PARK at 2250/3250, you can eliminate the drive shaft as a suspect. Since it happens at 60/75 AND when revved in PARK - yet isn't affected by a change in engine rpms while moving, I suspect the problem may be related to air movement. I'd suggest a thorough check of everything around the grille, behind the engine cooling fan and all of the air intake system. I'd also check the heat shields on the exhaust manifolds - even the catalytic converter.

Frank