Just guessing, blown injector gasket, bent push rod, valves not seating all the way. My uncle said he has a blown injector gasket because of all the gunk built up around that injector. Any truth to that...
I think I have the same issue (minus the white smoke) and I JUST replaced the cps with the black one from riff raff. I'll see how it runs when I leave work. It did stumble under light acceleration, but pulls very good under firm acceleration. So just in case I'm doing pricing for rocker arms, push rods, and valve springs.
My uncles 99 F250 did puff out clouds of white smoke under normal accleration but would clear up if he got on it. Then he went to start it one day and you could hear a open vlave. He pulled the valve covers and a push rod (or half a pushrod) was laying on top. After he replaced that one, another one broke and a rocker arm. So he just replaced every one of 'em.
Try running some tests on the engine and see if you get any codes...that'd be a good place to start.