Any of the Froyo based roms such as Beastly-Clemsyn (my favorite, very fast and stable), Frankentab, BC, etc all have working hardware acceleration, as does the new ICS beta. You are probably right about the hardware accel. being the problem, this is the same reason I always end up back on a Froyo rom. I have encoded a lot of video that I stream from my main PC, and there is almost always skips, freezes or audio sync problems on roms w/o hardware acceleration.
You can also try on your current rom, MXPlayer and Mobo Player have versions that are optimized for ARM v7 (Gtablet). In the players settings, change from hardware to software video and audio decoding. Most of my videos play alright with MXPlayer on software decoding using CM7, which doesn't have hardware acceleration.
Last, you could try Qloud Media, if you have a pretty fast PC. Qloud will re-encode and stream your video from the PC, optimized for the target device. It works very well on every device I have tried it on, and can even work beyond your network, but it consumes my entire 4 CPU cores in bursts of a few seconds while it is re-encoding, so no intense PC usage while it is running.