I just finished a few tailgates tonightl. Apparently trailer hitches were a popular thing a few weeks ago. Anyways, here was my process.
Pulled dents,
filler - knocked down with 80 then 150
1 coat of spi epoxy
3 coats of 2k
I then blocked that down with 80, then 150, using guide coat of course, lol
Went down through to the epoxy in a few spots.
2 more coats of 2k, 150,320,500(palm sander with interface pad)
spi reduced 1:1:1
dupont black
2 wet coats fo SPI Universal.
Anyways, these are production style jobs. If they are glass flat with no peal they wont match the trucks. Ill just buzz them with 1500 tomorrow night and wheel them.
But yes, anything finer then 150 when blocking primer to make it straight is useless. I gotta make a nice block. I have a paintstick thats been with me for awhile.. Thats always been my tool.