Questions about a high mileage TRD OR

I'm looking at buying a 2006 SWB TRD Off Road that has 215k miles. I'm not really sure what to look for in a 4WD, this will be my first. I've been reading a lot about the Tacomas and know about the frame recall and possible head gasket issue on the 4.0. How can I test and know for sure that the 4wd and 4-low work, besides putting it in 4wd and 4low to check for whining or grinding? That's mainly the only thing I'm not really sure on testing during a test drive.

 

If its in 4wd and you try to take a sharp turn on pavement, the truck will start bucking. Not great for the truck, but it will tell you for sure that 4x4 is engaged. Dont go crazy, just slowly roll forward and slowly turn the wheel. As soon as you feel it, back off.