I have an '83 ZXT and I tried an ecu out of a '81ZXT and there was no difference and the '81 was an auto and my '83 is a stick( 5SPD) They were not that sophisticated of a computer back in the late '70's when they were designed, and correct me if I'm wrong but they have no moving parts, they are just a simple board so clean it with alchohol inside and the conector, both the male and female ends. As for your problems with the RPM's I too had the same problem and no one came to my rescue with an answer, it got a little better but it cost me a chunk of change, and I'm still not satisfied!
ZRube
ZRube