cut out problem about 4000 rpms-any answers?

[klzemx3]

I have a klze in what was a 94 mx3 with a 4cly auto, I converted it to a 6cyl manual about 2 years ago, and kept the stock body harness, just changed the engine harness, everything worked fine except the speedometer and the a/c, about a year ago I put in the klze, and then two months ago i decided to change the body harness to control the manual tranny hoping it would fix the speedometer problem, now when the car rev's above 4000 rpms it starts to cut out, mainly when it is in gear and you are driving it. If you rev it fast it will go all the way to 7000 or so, but if you try to hold it at a steady idle, or if you are driving that is where it has all the problems. I have a new dist now because I thought that was the problem, but it is still the same. Anyone help with this or heard of this???