I've never know 5.4 to be dead vertical. Having just climbed this yesterday, and even using the tree, it feels harder than 5.4. Given that bark is slippery, for chimneying, an increase in the rating seems justified, perhaps bumped up to "Roper 4th class" difficulty.
Doing the route without the tree, is probably 5.8 or so. Downclimbing without the tree seems harder.