Unique egr concern

[Maxtegroom]

I am a diesel tech I had a 6.0 come in with intermittent black smoke and power loss.. No big deal I replaced the coked up egr with new and cleaned passages with a lil bit of carb clean and mostly a pick... Took it for a test and it went great a lil white smoke at start up but went away.. Well after a half hour test drive I parked it. Three hours later the customer picked up and drove off and I noticed a lil bit of white smoke from the tail pipe as he drove off I know for a fact his cooler is good. Could this just be risidual from the egr passage cleaning.. I don't know why white smoke is now coming out Amy thoughts?? Comments??