This is normal. My '06 Taco and my father-in-law's '06 Tundra both do it. These trucks have computer-controlled engine braking. I'm pretty sure it's described in the owners manual. It was discussed in this thread:
http://www.tundrasolutions.com/forums/tacoma/86260-i-need-gears-101-a/
I think with time you'll learn to like it. It makes it so you can tap the brakes to get down to 42mph in a 35 zone, and the engine brake will keep it at 42 the whole way down the hill without any need to hit the brakes again. It's a fantastic feature, IMO.
http://www.tundrasolutions.com/forums/tacoma/86260-i-need-gears-101-a/
I think with time you'll learn to like it. It makes it so you can tap the brakes to get down to 42mph in a 35 zone, and the engine brake will keep it at 42 the whole way down the hill without any need to hit the brakes again. It's a fantastic feature, IMO.