Had a look at the raw file, and i am also unable to get the channel swap to work. And as you mention, the trees arent as white as id expect.
The tree's not being white can be down to a number of things.
The time of day and and type of tree for starters, also as the leaves on the trees become older, they have less chlorophyl in them which reflects the IR light which causes them to be 'white'
I have always found that my best IR images, are taken either in the morning 9-11:00 ish and 3-5:00 ish, and i will alwyas try to make sure that the sun is behind me if possible.
Some times i have found that some days are just not good IR days, never found out why, but even with 60 seconds shutter speeds the images are just flat.
As for why the image of yours wont channel swap, i have no idea as i have never encountered this before. Though i suspect it will be due to avaliable IR light and atmospheric influences, just as some days when the isnt a cloud in the sky, but even with a polariser the sky just wont give that deep blue that you expect.
One thing that i would suggest is to find a lacation with several tree's and grass as well as a building or two, preferably on a day with the sun behind you and id imagine that you wont have any problems.
Id also use ISO 100, as opposed to 400, as this will cut down noise.