I cannot help you resolve your problem.
But as a matter of information I feel most people put too much timing in their engines which yields less-than-optimum performance. Adding compression, increasing volumetric efficiency through better induction and cams, adding blower OD, adding nitrous all usually mean you need LESS timing than stock, not more due to increased flame front propagation speeds, especially in view of advancements made in fast-burn combustion chamber technology. Igniting the mixture early produces negative work as you are building cylinder pressure with piston travel on the way up. The only exception I can think of is when a big piston dome gets in the way of flame travel, slowing things down. Big domes are passe anyway.
Taking timing out from your current timing seems directionally correct, with or without N2O. Keep working at it. Check your rotor registry.