I hope someone may know what this problem is..

I have a 1991 civic ITC race car.

At rpms around 3500 to 5500 I (seems to be) lose a cylinder, not sure which cylinder! I have done all the obvious including checking the valve lash, which I had adjusted. I have put in an MSD ignition, changed the spark plugs several times, checked ohms on plug wires, rebuilt the whole distributer and changed computers.
I'm getting nowhere with the car and it only seems to get worse. Any help with this gremlin would be appreciated.
Thanks in advance.

Devin
ITC#12