I think having "smooth scrolling" on can cause this. �You can turn it off in System Preferences -> Appearance.

>2 - On a muli-page file the PgUp and PgDn keys have weird behavior:
instead of scrolling up or down a page at a time, the window jumps all
over the place. �For example, on a 5-page textfile and starting with the
window about 4 pages down, hitting PgUp puts the window at about page 2,
hitting PgUp again puts it at page 3, hitting a third time puts it at
the start of the file. �This makes no sense to me at all. �OTOH,
clicking on the scroll bar moves the window one page up or down as you
would expect. �What might be causing this behavior?