[racket] DrRacket sluggishness since upgrading to 5.3.1 (OS X 10.6.8, 64-bit build)

Since I installed 5.3.1 -- I'm currently on 5.3.1.5 -- DrRacket gets
slower with use. It's snappy enough when first started, but after a
while, it gets sluggish. Switching tabs (and I have only three open)
takes two to three seconds, and scrolling pauses frequently. The
garbage collector seems to be getting quite a workout. (I'm not using
a memory limit, and my machine has about 3.5GB of RAM free.) Disabling
online compilation doesn't fix the problem.

I just noticed that scrolling a buffer brings DrRacket's CPU usage up
to 100%. I don't know if that's common or not; I've never checked
before.

I saw Robby's post on the PLT blog
[http://blog.racket-lang.org/2012/11/drracket-now-more-responsive_15.html].
Are the changes described there in 5.3.1.5?

-Jon