Should not have done #2 and 3 ... Shellac (alcohol-based) KILZ or clear shellac would not have required sanding because unlike water-based it doesn't raise the grain.

Sanding off the primer means you are back to unprimed wood in spots, so of course you get blotchy there.

No need to sand again:

Use your fingertip and smoosh a white wood filler or spackle into the hole.

WIPE off the excess with a damp sponge.

Thanks, I'm good on filling the nail holes.

Since I did #2 and #3 ... and still have another coat to put on ... any suggestions on how to ensure that the final coat is as glossy as possible without streaks/blotches?

I do not have a raised graining issue.

It's been a long time since I used latex gloss on anything, but I think it is very difficult to apply with any roller/brush and have it come out looking good. This is why we stick to semi-gloss or satin. You may want to try just rolling it and leaving it be (no brushing) or at least roll the paint on and then brush the paint out. The reason you may be having trouble with blotching is because the paint dries very quickly and you are going back into areas of the paint that have already started to set up and when you do that you are pulling the paint off there. You really only have about 15 seconds and then you need to let it be. Work in small sections which should be easy with flat trim. You may also want to try some Floetrol or XIM to help add wet time to the paint.

What product are you using? SW Gloss what? I have understood you have just one coat of topcoat? You need 2 coats for an even appearance, minimum. Why are you filling holes after the first coat of gloss? That should have been done after priming. As for primers, oils are the best because they sand smooth. Zinssser Coverstain are professionals' standard.

If you problem is streaky/uneven, then you need more build.

Some Waterborne/Alkyds paints are really good at leveling, but a complete brush-free finish is not realistic. SW Proclassic is as good as it get. I've had good luck adding a heavy dose of XIM extender to extend open time.

The best finish I have done with a roller/brush is BM Advance in a headboard and was applied heavily. On vertical surfaces it runs easily.

I hope this helps.

Thanks Paintguy: That helps a lot (especially the 15 Seconds part). I was working quickly but not that quickly .... and ... I went lightly down the entire 8 Ft length as a last stroke which I am estimating was at about the 2 minute mark (I am sure now the paint was setting up -- probably my BIG mistake - silly me, I was thinking that .... if my brush strokes show ... at least they should be straight)!

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Thanks Carlos: I am using SW Proclassic Interior Acrylic Latex Enamel (always) but first time trying Gloss vs. Semi-Gloss on trim. I am priming and 1st coat before cutting, nailing and installing (to limit ladder work for my old hip). After I assemble my whole frame including a corner molding, then I caulk and -- I do a final coat. I have done 5 doors and 3 windows this way with success (using Semi-Gloss) see photo below.

Thanks to both of you -- I'm using the extender next, working faster, NOT going over my boards a final time .... and will try the roller with a brush-out on an experiment baseboard. If I get a good technique w/extender, I will try the brush only with another sample board too.

Photo of my application (different room w/contrasting colors)

My inspiration Photo (white on white) -- my GOAL !!