Vocals sound slightly high pitched?

Suppose I do get a strobe light, check the speed, and it's running fast...what do I do then?

My TT's a Denon DP 300F.

Sorry for updating this a month later, haha. I've been pretty busy and forgot I ever made this thread. Today I decided to play a record on my turntable after resetting the tracking force and anti-skate, and the problem's still there. Then I remembered that when I first got the turntable, the belt slipped loose, so I ended up stretching it a lot (because I didn't know what to do with it/where to slip it on) before finally figuring out what it was supposed to do. I don't have a strobe light at home, and am too lazy to make one out of a flashlight, so I'm going to go ahead and buy a replacement belt from LP Gear, and see if that solves the problem.

Thanks again, haha.

Also, I should probably mention that I test-played a song that I was very familiar with. I pressed play on the turntable (as some of you may know, there's a slight delay of a few seconds) and as soon as the song started, I pressed play on my laptop. The maximum difference was less than a second. I had one earphone in my ear and the other listening to the turntable version. All parts of the song (guitar intro, vocals, a spoken word sample at the beginning, etc.) had a noticeably but not unbearably (by this I mean, it wasn't chipmunk-level but I could clearly tell the difference) higher pitch than the MP3 version. The song itself also played slightly faster than the MP3 version.

Also, I didn't exactly note the times, but the turntable version of the song was running quite a bit faster than the normal version. Halfway through the song (at around the 1:30 mark), the computer version was running 10-20 seconds behind (again, just an approximation as I didn't note the exact spot on playback).

FIXED :D
I don't know how this happened, but the belt had slipped off the outer rim of the perimeter and was just loose inside the turntable (yet luckily still looped around the pulley). Im still thinking about replacing it as it's clearly but it's good for now. Thanks everyone!