Well, your first tune up had a 10 pill spread on the jetting. I don't have a lot of Nitrous Works numbers, but what I do have, shows that to have a N/F ratio of 4:78.1, extremely rich. You also had a little too much timing. 28* was too much for that amount of nitrous, but you got by with it, because the tune was rich. Now your second tune only had a 3 jet spread and the N/F on that was around the same ratio, but you don't say you pulled anymore timing and the plugs looked gray. I suspect it did not pick up with the second tune, because it was overtimed and detonating the motor. You should really be careful with this motor on spray. You have KB pistons with extremely tight ring gaps. If those are hypers, you are asking for trouble. If they are indeed forged, the gaps are still tight.

Monte