I have a 2002 4Runner (the V6) that sits for a few weeks at a time between uses (I live in coastal FL). If I haven't started it in a while when I put it into Drive the gears don't seem to engage unless I rev it a bit and then it "clunks" into gear (reving it up in Neutral has no effect) . After I have done this once, it runs fine until I don't run it for a while. My wild guess on this is that over time the transmission fluid is draining out of the hydrolic actuators that shift gears and that I have to rev the engine up to push that fluid back into the lines. FWIW, I don't appear to be low on AT fluid.