Low rpm with sn92

HI, newbe here thanks for all the info. ya'll have posted througth the years. Wish I'd fond this form 5 years ago. Just going from stock 302 W/ 69w head and sn92 to 347 W/ track 1 brodix heads. Motor n/a made 440hp @ 6100 on 93 octane. Installed sn92 Made 519 @ 5900 w/5# boost. We've tooned out motor on a land & sea dyno so air fuel, timing all sorted out. Is this normal to lose peek rpm?

figure the sn92 is only good till 39k rpms. from everything I have researched anything after that is just blowing hot air. what size pulleys?

5.75 to 3.75 Had 3.25 before

So at 5900 rpm the sn is spinning at 39805rpm which is were its getting hot, are you running a cooler of any type?