Painted the bumpers TWICE already but it won't last

Yeah so I've painted the black trim around the front and black bumpers two times already, but within a month, they look like CRAP. The first time I used the duplicolor bumper paint. It looked awesome....for a few weeks. Then I started to notice little places where it was peeling and you could see the ugly gray/purple-ish trim. It just got progressively worse and worse until it was half gray and half black.
For try number two, I decided to use duplicolor trim paint as I used it on my grille insert and rear pillars and it still to this day looks great. I also opted for an adhesion promoter on this go-round. Again, within a month or so, I noticed it was peeling. And it seems like every time I look, more and more has peeled.

So I need to know, what the hell can I do? Both times I did prep work. I washed with dish soap, scuffed it, washed it again, then used a degreaser. I'm just at a loss as to how I can keep it looking good for more than a month! I don't expect the rattle-can job to last years, but more than a month isn't too much to ask, is it?
I was thinking of using automotive paint and having my dad paint it with his paint gun.
Is there some sort of prep work that I'm missing? Or maybe a better brand I can use? Would a clear coat help?

Any advice? I really hate the ugly gray, but black peeling with ugly gray is worse.

 

[Joe Dirt]

That does look nice... I used shoe polish on my black trim around my old '86 Thunderbird before it was traded in- works great.

 

[Sams01XplrSprt]

looking good keep up good work