The plugs are probably a good place to start. Also, I would recommend adding a bottle of Bars Stop Leak into the Radiator to hopefully plug the hole from where the water is going.
Then I would just keep it topped up on fluid and drive it til she dies.
A lot of the items I listed are some of the key things to keep up on if you want the truck to last +150k. If the Tranny fluid really hasn't been touched in 135k I wouldn't touch it now since it is already on borrowed time (they really need to be flushed every 30k).