severe orange peel in my paint

I have a 91 corvette. I sanded the original finish with 320 grit sandpaper, cleaned the surface with wax and grease remover then tack clothed after prep. sprayed a mist coat of black epoxy primer then 2 wet coats with only hardener. the last coat of epoxy, I added mid temp reducer as directed to create the sealer. before applying sealer the primer was slick but lots of orange peel. after spraying the epoxy reduced as a sealer everything turned a nice dull black and was really smooth with no orange peel. 3 days later I tack clothed again and sprayed a single stage black urethane paint on with mid temp reducer at about 63 degree air temp.I test sprayed a bunch of old slick parts first and let them flash and the finish on the old parts came out nice and slick the way it should look so I sprayed the vet with those gun settings. the paint severly orange peeled in the end. for the 3rd coat I tried adding a little more reducer to smooth the finish but with no luck. what went wrong ?? why did the parts come out great test spraying but the car did not ? can I re-sand the new finish and try spraying again till I get it right and if so what grit of paper do u reccomend to re scuff for another try ? the gun was a 1.4 mm tip HVLP gravity feed and the pressure regulator at the gun was set on about 40 psi so I could get a consistent 35 psi. any help would be greatly appreciated.

You may try turning your PI down to 20 PSI. Try this and see if it helps.

HVLP = High volume (paint) Low pressure (air)!

Sometimes orange peel is also cuased by using the wrong thinner { under diluted }. With a fast evaperating thinner it will cause atomized to be dry before they hit the surface.