I sent you a PM on e30tech on this.
Give using 4.0 ms a try, but I don't think your problem lies there.
You should try BR7ES instead, or just plain B7ES even though the lack of a RFI damping resistor can cause problems depending on the ignition wires.
The 'P' stands for protruding center electrode which makes it easier for the cylinder pressure to put out the spark.
What ignition wires are you running?
It must be clinically clean inside the plug holes and the wires must be dirt free, no oil or crap anywhere.
If the wires are subjected to a lot of heat from the exhaust manifold the insulation wears out quickly and the spark can jump through the insulation where it has dried through.
You should upgrade to the latest firmware, which could be a challenge since you throw away all your MegaTune knowledge, but it's not a big sacrifice - trust me. Use 1.1.85 (the latest), only some idle control enhancements have been found but not yet released (1.1.87).
With more recent firmware you can use "MAP scale" which adds dwell with higher boost, so you can still run 3.0 ms basic dwell, and go up to 4.0 ms at higher boost only.
