Problem with downloading HD movies to Mac when syncing with iPad 3 I bought several HD movies using iPad3, however when I try to sync my iPad with MacBook Air (i7, 13", Mid2012) they are downloaded with much lower resolution to my Mac. 

I don't know also I this is connected, but I don't see them in iCloud (no iCloud icon next to them in iTunes, so I'm unable to re-download them once deleted, all I can do is to sync with iPad 3 but with low resolution)
You're looking at the wrong file. Open iTunes and go to playback (iTunes > Preferences > Playback). Set it to play the HD (1080p) file by default. Just because it is the default downloaded HD version, doesn't mean that it will play that one by default.