Well, I read your story, and I think you may need to lay off that little Overdrive switch. auto trannys are not good engine brakes. Manuals are not good ones either. Proof that brakes are cheaper than transmissions. Last i checked the Xterra's braking ability is awesome, even with the drums in the rear, 4 people and all their crap.
the only vehicles needing engine brakes are big rigs aka 18+ wheelers, one of my good friends blew his tranny 2 months after he discovered that switch. :rolleyes:

brakes = cheap fix
tranny = expensive fix

I drive a 5spd with 130k, and I'll burn my brakes before i down shift

on the other hand you got 170,000 miles out of a moderately abused transmission, go nissan.