If there was a plumber involved with the installation, have they considered a partial blockage of the drain line for that toilet? The vent line for the toilet may also need to be checked for blockage. Something is not allowing the flush action to work properly and those are two common problems.
Also, the model number you gave is the number of the tank only. Has the bowl been replaced as well. If not there could be a defect with the bowl.
Vent line and the drain line were both checked when the first new toilet went in and again when the replacement one went in.
Sorry about the model number, but both the bowl and tank have been replaced twice. The toilet is one of Kohler's new "high efficiency" 1.0/1.6 gallon flush units.
Although it 'looks' the same as the other elongated bowl/comfort height toilet in the other bath, it is a loud power flusher.
The real problem is that although the water flushes quite rapidly (the first time I thought it might take my arm off) the water does not "sheet" down the bowl, nor does it swirl around the bowl. As a result there are narrow wet streaks that run down the bowl, leaving the crap in vertical striations where the water never runs.
If this is a Kohler problem I guess I'll have to take it up with them (which I thought I was doing on this site)