@david264
Hi. I agree that sometimes taking a step back can help.
I don't know what you have referred to in the past, or what guides you have read, so I post this in case its helpful.
The Retropie Docs offer some good guidance (link below), the bits on testing mouse inputs and determining mice index numbers might help.
https://retropie.org.uk/docs/Spinners,-Trackballs,-Lightguns,-and-other-Mouse-Devices/
Have you installed the gunconf utility? It could be the gun calibration that is the issue. this also lets you test the gun.
https://github.com/gunpadawan/gunconf
This thread (link below) has a whole load on informaton that is related to the issues you have had. I have provided part of the thread below which specifically mentions the sensativity issues.
https://retropie.org.uk/forum/topic/21848/aimtrak-gun-loses-alignment-when-i-aim-off-the-screen-tag-aimtrak-tag/70
I hope that helps, and I can try and answers questions if I can