I know there have been several threads on changing the serpentine belt but I did mine recently and put together a DIY guide based on all the stuff I found.
My advice when attempting to install the new belt, start with getting it around the crankshaft first and work all the pulleys in order and end with the fan pulley. I went with the Gatorback which is a snug fit so i had to be specific in the order. The Tundra or Land Cruiser belt is probably long enough that you can skip my advice .
The tensioner is pretty strong and a longer handle on your wrench or socket makes it easier. I cheated and used a long handle breaker bar and socket to move the tensioner. There is a hole on the tensioner to lock it in the released position. This hole is about 2-3 inches deep and about the size of a pencil. What I didn't know was that the hole is horizontal.