On the 99-06, the crew cab's rear seatback folds down for cargo (seat bottoms flip forward, like the 2nd row on LWB 370s) while the ext'd cab's seat bottom folds up, instead.
Reason I mention is that with the ext'd cab's seatback permanently affixed to the back wall, it's nearly vertical compared to the crew's. I believe it's thinner (less padding) too, although I'm not positive on that.