My issue with GFCI was due to old wires that were either nicked, exposed wiring due to insulation raveling, or simply just showing some corrosion from the moisture over a 15 year span.
I replaced the last 8 inches or so of the old wiring with this new 12-15 inch strip and everything is now grounded properly per code and NOT tripping the new GFCI.
You can see where I used a Marine grade heat adhesive shrink tubing.
Note: This problem should have been noted a long time ago had the original electrician installed a GFCI as he should have. That old receptacle box is only 5 feet from a pool !!!
I never would have known until I just happened to want to add a new box in another area on the other side of the yard. This was necessitated after the Gate Installers accidentally cut a buried wire going to old receptacle. I kept thinking it was me or an issue with brand new GFCI, but the GFCI did what it is supposed to do, help save lives by telling you something is wrong.
Incidentally the new GFCI box is inside the fence, and on the opposite side of fence is RV. It has 20 amp receptacle on it's 100 amp subpanel, but it is nice to have extra power outlets when you are outside.
Thanks all for the help.