Maybe it’s the rom? I had no problem with it. I’m not even running a BIOS for it right now. You are running the latest Retropie (3.2.1)? Have you tried using any of the other emulators for tekken to see if that could be a solution?

According to HerbFargus’s first link
gpu_mem_1024=256
overrides
gpu_mem=64
so I’m at 256 split, so if you have that in your config.txt for boot, that could be why you aren’t seeing any changes with changing the split.