We paint our roofs white for the Texas sun. On my '99 and '00, I used Rustoleum and it still looks fine. On this '04 I used Tractor Supply house brand Majic paint. It started to peel after 2 years, makes streaks down the windshield too. I saved a few bucks on that gallon, but now I have to remove it. Don't buy Tractor Supply Majic paint. Anybody know how to get this crappy paint off without damaging the underlying paint? I figure this time I'll wrap the roof. We have the Texas star wrapped on hoods of company trucks, and it comes clean super easy, 4 years and it still looks new. It figures, our only 6.0 is the one with trouble, lol. But this one has been good, ARP/delete, not tuned, and only 1 injector and 1 hpop have failed in 4 years. Both failed a couple months after install. For a 6.0 that's not bad. I did throw new injectors and hpop on it when I bought it, got it cheap with the cab off for studs. That tech quit my buddy's shop, nobody wanted to finish another guy's job so it sat there, and I got a deal.
I'd make fun of you for owning a 6.0, but I own a 5.4 gasser of the same era- so who's the fool? Paint is all about prep, and it doesn't look like there was much done on the roof before you shot it. No primer, no sanding, maybe not even degreasing? Maybe a silicone spray used on a windshield install? That said, TSC paint is crap in my experience. Sand it down and paint it up.
I think a pressure washer would peel that off without much effort.
We paint roofs with a brush. Nobody can see it but me and my tall sons. Yeah we're 7.3 guys, PSD or IDI, and only have one 6.0 at the ranch. I do like the 5R110 a lot. But for towing or a long road trip the 7.3s get the nod every time. Carry a 10mm wrench and a spare CPS in the glove box ...
You could try lye, put burlap or some other fiber on the roof and saturate it with a strong lye solution, then keep it damp until the consistently scrapes loose with a fingernail, then pressure wash. Don't know what it would do to the rest of the cab, the factory paint should be fine. Otherwise, if you're just brushing it anyway, pressure wash it as best you can and if a pressure washer won't take it off, it's stuck good enough to paint over.
I love my 6.0 I'll take it anywhere. Maybe try a wire wheel if you going to paint over it. Maybe a scotch Brite pad on a random obit with polish products.
Second the pressure washer, we've stripped better paint with a 3,800 psi and a turbo nozzle.