I suspect the answer lies within your post.
After choosing the right medium for the steel, angle is the most important aspect of sharpening. I'd say you're seeing more success with the Gatco because it is helping you maintain an angle which by extension would mean you're not getting or maintain the proper angle while free handing.
As said, use a marker to mark the edge bevel and adjust until you're removing the marker form bevel shoulder to edge. Re-mark as you adjust your angle to make sure it you're getting all of it and not a little here and there as you adjust. You may find spots where it doesn't all come off and that is usually inconsistent grinds that will need to be sorted out throguh re-profiling or over repeated sharpenings.
Go slow and don't concern yourself with pressure. Default to lighter is better, especially if using diamonds. Some stones like a little more pressure but that's nothing to concern yourself with now.
Get sharp on a lower grit.