I'm learning how to do any% as my first Ocarina of Time speedrun. Right now I'm learning how to do GIM in Deku Tree. When I try to do dive cancle I hear both the C-Up sound and Link diving. When I cancle C-Up to start swimming to the vines, Link suddenly surfaces from the vines. I've tried pause buffering to make sure I press A and C-Up on the same frame and this still happens. Anyone know what I'm doing wrong?

I'm not entirely sure what you mean (but i also play on n64 and am not very good at gim Kappa) but the forums here on src are not that active, all the activity is in the discord server which is linked on the left of the screen. You'll get a faster more accurate response if you ask in the any% channel