Intermittent Smoke

[erthwrks89]

I have taken the truck to a International dealer which has worked on the truck since 1995. They checked everything out and even called the rebuilder where we got the second motor from. They said it could be the turbo , we replaced the turbo but still got the smoke, but the performance and mileage seem to get a little better . Its smoke the worst on shift points 2-3 & 3-4 but its not all the time . Its hard to tell but the smoke seems to black at shifts and gray on when you just floor it. I pull a 20 ft trailer 10'6 high all the time. Any Ideas ? Thanks Bill