As I said in my other post, don't map "G" to anything.
Map the Toggle Landing Gear Up/Down under A-10C Sim / Systems / Throttle to JOY BTN15 on the Throttle (that's the Left Throttle Button).
Open Options, click on Controls, select the A-10C Sim dropdown, select the Systems dropdown, scroll till you see Toggle Landing Gear Up/Down, click the field for that selection under the Throttle Column to highlight it, click on Add at the bottom, press the Left Throttle Button till you see JOY BTN15 fill in the key field. Click OK, click OK, enjoy.