Mods, if this belongs in tuning, feel free to move it.

I have the timing tuner and am using the window switch for my nitrous system. I'm trying to add a little timing when on the motor, and pull it back out when the nitrous is on. I'm trying to get to 2500 as soon as possible, so the fun can begin. Here's the problem. On the motor, when I try to add more than 3* timing advance with my timing tuner, I get a P0300 (random misfire) code at around 2800 rpm. Below or above that, at full throttle, or idle, it doesnt do it. If I hold it there at 2800, I will get that code, i.e. driving at 80 on the freeway will do it all the time. If I slow down and drive for a while, the code normally goes away. I can run 3* advance all the time and never get it to throw a code, but when I try 4*, it pops up. Does anyone know what can be causing this? It has a stock tune, and NGK TR6's gapped at .035. Thanksin advance.