It is probably the filters. The last time that I have any proof the filters were changed is a piece of tape under the hood with "Fuel done at 32K" written on it. So if that is the last time they were changed, it have about 33K on the filters. I will pick both filters up this weekend and change them out.
I do get smoke from the truck on a hard acceleration, as the turbo is spooling, It is just a light haze though, I can see it better at night in the headlights of the car behind me. There is a light amount of sooting on the bottom of the back bumper, not bad, just looks like it is a little dirty.
It is a chunk kind of sound. It sounds like there is almost a pause, like the drive line is relaxed for a second. It is similar to the sound when you shift from reverse to drive, or if you are parked on an incline and take it out of park. It is not that "hard" of a sound though. It is only something I can hear, there is no "feel" associated with it. The thud is only on a medium acceleration, shifting from 3rd to 4th. I don't notice if I am easy on the throttle, or if I am getting after it. But under a fairly normal, away from the stop light and get up to speed kinda acceleration.
I hope that I have not rambled on to much. But I am computer admin and I like all the info I can get. Ask Trav, (argve) I can get detailed when giving info. He and I are good friends, I am just a littler easier on the equipment.
Thanks,