MMC1 runs in slow motion problem...

I'm having a bunch of issues with an MMC1 board i'm working on. It uses the original MMC1 chip (MMC1B2 to be exact), and I'm just using it for fooling around with. However, i've run into an issue...Legend of Zelda seems to run in slow motion intermittently on my FC-Twin system, but seems to work fine on a original console. The game will be working fine at first, but then it will start to chug and slow down (including the music)...but the game doesn't stall. It speeds up and slows down like something is playing with the throttle. I figure this might be a PRG-RAM issue somehow, but my board is wired up identically to an SNROM board. This does not happen on a INL cart or the original game cart though, so it leads me to believe it HAS to be something wrong with my board, but what would cause this? I should add that this doesn't happen on any other type of MMC1 game...SKROM, SLROM and even other SNROM games (like Metroid) all work perfectly. Just Legend of Zelda has this issue.

TL;DR - Zelda runs in slow motion intermittenly with audio lags but doesn't stall. What could cause this?

This could be a problem with the voltage supply since many cheap famiclones are incapable of well distribution of the current. Try placing around some capacitors and diodes in your design.

I'll try that and see if it makes any difference.

Thanks!