My 2000 has the 3rd row and that same area too, and it definitely has a latch of some kind on it. I think I agree with the idea that you might have to take the handle out first to get to the area you need. I'll look at mine and see if I can see anything that might get it open if the handle wouldn't.

 

it is standard for these trucks to have that storage compartment up against the rear liftgate(in the floor of the cargo area) the latch is angled from underneath, if you could get an old credit card or something similar through you may be able to just push the latch in and get the top open.