Car drives around fine and boosts fine. Except if I stay on it for more than just one gear it'll start smoking greyish white, and it'll keep smoking until about 5 seconds AFTER I've let off the throttle. Never smokes any other time. One of my turbos on its way out?

 

I'd say so.

 

Most likely yes however, first change your plugs and see if it helps. Sometimes a fouled
plug(s) will have the same symptoms. And do lots of searching too! Good Luck