I just replaced mine and it's pretty easy, helps to have someone inside the truck. I purchased the replacement mast at the Toyota dealer, it is a universal part. Loosen the chrome ring and when you start the vehicle the antenna will start to go up just keep pulling it and the person inside should push the UP on the power button to extended all the way. You should notice how the teeth are facing when you pull out the old. Insert the new mast as far as you can and the person inside should turn the car off so the motor grabs the teeth and pulls the mast into the fender. Make sure you put the chrome ring on the mast before inserting and tighten it after the mast has been pulled back completely.
Next time I'll remember to lower all the way when going through the car wash!