350 engine WOT loses power at top end

[ProStreet83C10]

Hey guys, i noticed this spring after i stored my c10 all winter that when i go WOT and get to the top end of 2nd gear my engine just falls off on power, almost like something has cut fuel or ignition. as son is i get out of the throttle it comes back and i havent kept my foot in it to see if it comes back or not.

what do you guys think the cause of this could be? under normal driving/throttle conditions the truck runs 100% fine and this only happens what at or very close to WOT.