Shifts hard sometimes

So I bought this vehicle a couple months ago and I first noticed the shifting problem when I drove in the rain. It went from shifting smooth as can be to running about 1/2 rpm (2 to 2.5) higher than usual and shifting hard into the next gear. It would do this on every gear for a short time (five minutes or so) and then just seem to work itself out and stop. Over time the issue does not seem to be rain specific as it now does it on a daily/semi-daily basis. The transmission in the vehicle was very recently completely rebuilt so I do not think that that is the actual problem. (It is a 5.8L not a 3.8)