Frustrated with inability to do body work!

You just need to get it close enough for a high build primer (which is fairly close).

Careful blocking of the primer is what makes a car straight.

I will agree with this statement. It appears you had it close at one time but kept sanding because you were doubting yourself then went too far. It's a fine line of stopping or keep sanding. I've found that when I get to the point I know it's close I shoot a few coats of high build on it, then some guide coat, then lightly block with 150 to see how far I am off. Trying to blend "mud" into bare metal can trick your eyes. I'm betting you were closer than you though at one point. Keep at it whereas I can tell you have the right idea.

-Jason

EDIT... sorry I didn't realize I hadn't read the last page but I'll leave this comment up for others.