All good advice here.

One other thing to check is, are the elevator halves moving symmetrically? I seem to recall that this airplane has separate elevator halves driven by a split (Y) pushrod. If the pushrod is not adjusted properly, it could be moving one half of the elevator more than the other.

However, that will cause a roll; and what you describe sounds like a thrust problem. Serious aerobatic pilots deal with this by either altering the engine thrust line, or mixing the yaw out. The latter requires a rather sophisticated programming capability; otherwise, the mix will interfere with "normal" flying.

Anyway, check your elevator travel; you never know.