I just bought my GF an X-90 with an auto transmission. Compared to my X-90 with the standard transmission, the automatic is gutless and mushy. I want to swap out the automatic and put in a standard. The mechanical aspects are obviously pretty easy... Are there any electronic issues that I need to be aware of like the ECM being different, etc?

Thanks.

The ECMs are different, but an auto ECM will run a manual tranny fine.
The pigtail that goes from the engine part of the harness, back to the tranny is different between an auto and manual.  So you need to get that section of the harness for the manual tranny.  Just unplug the auto tranny harness and plug the manual one in.