Different factory turbos?

[97-6.5TD-F]

Was reading on here something about different turbos on the 6.5? GM 4 and 8 or somthing? Could someone elaborate on this for me?

[More Power]

The GM-series of turbos somewhat followed the model year... For example, a GM-3 was used on the 1992-93 models, the GM-4 on the 1994 models. Sometime about 1997, GM began using the GM-8. Each series number represents a small evolutionary change from the previous version, though the GM-8 is perhaps the most changed from the previous ones, though it too represents just another small incremental change. The best, in terms of efficiency, would be a GM-8, but I would not spend the money to upgrade (replace) a perfectly good earlier version.

Jim