Re: Star Trek III - The [Speculation Begins] (Spoilers)
TMP was number 1 for at least the first 4 weeks of its release.
BoxOffice Mojo only had the first three weeks of TMP listed, so you may well be right. But the point stands that only two Trek films spent multiple weeks at number one.
"I tell you what you all need, you need to take a thirteenth step, down off your high horse." - Hank Hill, King of the Hill