The T43 actually isn't too oppressive to work with. The newer ECMs (E38 / E67 / E78 / E83 / E92) need a GM dealer / TIS flash if replaced - as tuning software cannot read / write the throttle control portion (second core) of the ECM.

The T42 / T43 / T76 TCMs can be completely reflashed using tuning software - making them a little more user friendly.