An over oiled K&N can cause black smoke, read restriction. Does the restriction gauge still work? Does it read more than 25in of vacuum.
Remind me of the year model, 5spd or auto etc. 40 psi sounds kinda high for the oe turbo, you are testing its design limits, 34 psi max is a safer setting. Adjust the wastegate or the boost orfice elbow, if you are running a camplate etc. .
You might ck. the clearances / side play (radial clearances) of the compressor side of the turbo the spec. is (. 012-. 018")
The end play is . 004-. 006" before serial no 840638 and
. 001-. 003" after 840638. If you are having some oil consumption, the lube oil lubing the turbo maybe entering the intake (clean air) and causing en-richment ie the black smoke.
From your white smoke complaint in the am, I'm thinking overflow valve (low fuel psi).
How much oil does your truck use every 1000 mi. , 3000 mi. between changes 5-7K??
It's possible that the timing slipped. . but maybe not likely. Often when timing slips it slips a fair amount and causes more severe symtoms than you describe.
Could you have picked up a bad load of fuel? Low cetane can cause this too. Have you run any injection cleaner thru it lately?
The injection cleaner may cause it to smoke a bit more, until that tank of fuel is run down. .
bed time, now.
Let us know,
Andy