I have a ZZ383 GM crate engine with a TPIS mini-ram fuel injection system with 30lb fuel injectors. The engine management logic is speed density. I am having a problem with cylinders 7 & 8 running richer than the other 6 cylinders thus causing the spark plugs to foul out. I have a scanner and have determined that idle conditions contribute most to this issue, however overall I have been running rich as my block learn memory number was 108.  Initially my minimum air adjustment was at base minimum with the throttle blades fully  closed. I have sence increased my minimum air adjustment and re-adjusted my TPS in an attempt to allow for the availability of more air during idle. I have also backed off of my fuel pressue in small increments from 45psi to now at 41psi, and have also changed from conventional spark plugs to double platinum. My block learn memory number has increased to 118-120 at idle and from 120-130 during normal driving conditions. Does anybody have any thoughts or suggestions on this, have I gone about this correctly ?  

On the computer tuning I can't really help, but I'd suggest trying a heat range or two hotter plug in those two cylinders to burn up the extra fuel.  

Thanks for the advice 55. Has anyone ever ran different heat range plugs in the same engine ? Are there any risks by doing it ? I have never done this.