That faucet has an added friction point, which is where your problem may be. The rotating handle and the stationary "cone" are a single unit, and if corrosion has occured where they meet, it will cause hard turning. Remove the handle/cone and and see if the tightness is in it. If so, soak it in something such as CLR or vinegar, and then spray a lubricant into the groove before putting it back on. If that does not eliminate the tightness, call 1-800-4KOHLER and have then send a new handle assembly. The stem is a ceramic seal version, so they seldom become tight, although a swollen "O" ring seal might do it, (your statement that it seems to happen after running the hot water implies this may be the case, howerver), in which case call Kohler and have them send you a new one. You will not know where the tightness is until you remove the handle so you can try the stem and handle separately.