If using a USB cable, ensure the Prolific or FTDI drivers are correctly installed in your Device Manager. Step-by-Step Programming Guide
This is the version everyone wants. It runs natively on Windows 10 and 11 (with a few tweaks) and supports the GM338, GM3188, GM398, and PM400. motorola gm338 programming software free best
The CPS for the GM338 is designed for precision but has a steep learning curve for beginners. If using a USB cable, ensure the Prolific