DP90 is now DP90LF and nowhere near the primer it once was.
I like to use Southern Polyurethanes epoxy primer, turbo 2k primer and universal clear. Their black basecoat (and single stage) is one of the nicest blacks out there.
They have a great user forum where you can ask questions. Their tech helpline is very good too.
SPI is very popular with restoration and custom shops.
For poly primer I use Z-Chrome Rust Defender that I buy on eBay.