870 turbo overspeed cel

[tree98]

870 in a kenworth t800 with 422,000 mi. Demandated(Unilever) gets a cel when loaded and going through the gears. Been doing it for a while. It doesn't happen at any certain rpm but I did notice that when the light comes on the boost gauge is at 40 and sometimes a hair over. Isn't that to much boost? I know a turbo overspeed code could be caused by a boost leak but could it even make that much boost if it had a leak?