I've got two 3880's and they both skew odd at times.
I can put a square on the feed tray against the paper to make sure it is square in feeding, but once it grabs it, it might twist it off skew a bit - or not. My only solution is to feed it at a slight angle that I know might be better. On one, I wrapped some electrical tape around the flip-down post (It was found on dpreview for a while) on the pull-up feed tray to tilt the paper to the left a bit and it picks it up better without the skew issue. The other has a bit of a molding issue with the external pop-in rear feed tray and the skew is off on it almost always. If I switch it with the other's tray, it works better.
Just the nature of the beasts. Even with two of the same model, they have very different personalities. Even ICC profiles are a bit different between them too which is maddening.
SG