GD Archive Item - Change the length of the text shown with GD Loop and GD Listings
The GD > Post Content shortcode can be used to control the length of the post_content (Description) field display.
Use the Shortcode Builder to create a new GD Post Content shortcode to have the exact options you want.
Here is an example:
[gd_post_content key="post_content" limit="12" read_more="Read More..." alignment="left" strip_tags="1"]
Also, you may need to check in the Description custom field settings to make sure the Description field is not being displayed with the "Show in extra output location" option for "Listings".
You can find that option here:
Places - Settings - Custom Fields - Description field - Show in extra output location - Remove "Listings" if it is present.
"Show in extra output locations" is used to show fields in the GD Output Location Shortcode.