Shifting into 3 at 3000 rpms how to adjust

I like to snap a pair of hemostats on the cable about where I want that little block on the end of the lower cable so I have a reference.
Either that or a mark with a sharpie on the cable.
You want a bit more slack in that lower cable, so you could move the little thing with the allen set screw in it toward the front of the car, or even easier to adjust the cable more forward where it mounts in the bracket since it has room in it's travel.
I'll mod your picture and repost it in a second here.

Ok, either or but not both as a little change makes a difference.
Then see how you like it, and now you know how to change it.
If it starts shifting into 3rd at 15mph you backed it off too much . :D

View attachment 1715167853
Ok, thanks for taking the time to explain, I understand now.
The other gears I believe may shift ok but winter is just getting over here so I really don’t have much seat time in the car since I bought just before winter.