I have a 2005 Pathfinder SE 2WD (possibly off-road model - not sure) with around 80k miles and sometimes when I brake going downhill, the transmission shifts down to 3rd gear. It doesn't happen all the time. This only started a couple of months ago and I've had it since June 2009.
I tried pressing the OD off switch and it shifts back up to 4th. If I press OD back on, it shifts back down to 3rd. When the tranny has downshifted, I can also give the gas pedal a good tap and it will shift back up to 4th and then OD.
I bought the Pathfinder used with 50-60k miles and I have not changed the ATF. The level of ATF is normal.
I've read about the contamination in the radiator from antifreeze but my ATF doesn't have the "strawberry milkshake" look.
Wondering if anyone knows what could be happening.