GM 6.5 pump and chip calibration mismatch
The first 6.5's had different pump models (5067 and 5068) to differentiate between LD and HD. This was in 1994 with some potential overlap into 1995. These pumps required different "language" in the chips. Eventually GM got smarter and made the LD versus HD changes in the programming rather than in the hardware. They used the LD "language" format so that all pumps were interchangeable except the 5068. The 5068 is the only pump that requires a special chip. I find mismatches quite frequently and the owner never knew why the truck ran so funny or could run so good when set up properly. For this reason I recommend upgrading any 5068 pump to the latest 5521 or greater and making the appropriate Eprom change.
There are literally dozens of chip calibration ID's out there. The GM calibration ID’s are 4 letters long (example BMRM) and are printed on the Eprom and sometimes on the ECM case. Never trust the sticker on the ECM case as the Eprom may have been changed. I have an old list that groups them together. This list may not be 100% reliable, but hasn’t failed me yet. As I do more and more I try to match the groups to the appropriate pump model and update my list to show this. Since you no longer have the 5068 pump but apparently still have the OE chip there is a mismatch. This just makes the truck run a bit "stupid" in that it can stutter, hesitate, smoke bluewhite etc. This is cured with the correct calibration.
We offer a basic stock Eprom that corrects this issue or better yet a Performance Eprom that offers best performance, and value without any necessary “crutches” like manual wastegates etc.