Black smoke thru gears and Which turbo to run on 6nz?

Currently just got the injectors tested on this truck due to a problem of the truck blowing black smoke when shifting gears. all 6 Injectors are good. Injector guy says this is the 4th time hes heard of this problem and mechanic says he doesnt know what it can be. Truck gets good fuel milage and Truck isnt low on power but still on the original turbo which has probably over 3million kms. So we are going to replace the turbo even though that wont change the smoke problem. Got any ideas what the smoke problem can be ? and what turbo would you guys reccommend? Also its a 550 6nz currently at 475 on mild auto part runs. Need a decision by tomorrow. THANKS

 

no codes no lights. Basically, everything checks out good, haven't tested with a different ecm because we dont have one on hand right now. I mean nothings wrong with rolling coal but its a fld with one stack at the back and it only used to get the trailer corner super black now it even gets the truck black

 

Currently trying to figure out what already built turbo i can buy that is better than the stock one, dont want to build one buying the compressor, exhaust and cartridge separate. Main concern is fuel economy and not thinking of boosting the truck over 500 hp since thats not needed.

 

What injector trim codes would you recommend to run? trucks never got any aftermarket done, was rebuilt in 2012.

 

I've read here and on the diesel garage but i found 3 different part numbers and people recommend BW non wastegated 175963 which is a c16 turbo but they change the housing to an non wastegated? i Just want a direct bolt on. Will have to find one to put a pre low nox file in the truck but i want to know if that turbos to big for the work we are doing.