Not really. The 3.4L V6 is incredibly solid. Just make sure you do the normal checks you would when buying a used car. Engine oil (smell if it's burned, color), transmission oil (burned, make sure it's red and not brown or "milkshake"), etc. Make sure if it's 4WD you thoroughly test the transfer case (shift in and out of 4HI and 4LO, listen for clicks in the front end).
The only real problem I can think of is the real axle seal. Other people who have owned a T4R longer than me might know more.
For what it's worth, I bought a 98 SR5 4x4 with 160k miles 2 weeks ago and I absolutely love it. I've changed the brakes and headlight/tail light/dome light bulbs, plus a full oil change, and that's pretty much it. It runs awesome to be such a high mileage vehicle.