Transmission bump, not during shifting

When driving down the road and holding a consistent speed, lets say between 50-65 MPH for example, I will feel a single "bump" from the transmission. It is usually once every few minutes, so on a 15 minute drive I might feel it 10 or 15 times. This is not when shifting between gears. It is not very rough at all, and not audible, just a quick "clunk" feeling. It is only a split second and the truck never slows or revs or anything else like that, it just keeps going along at the same speed. If the road is bumpy or I'm distracted, I sometimes don't feel it at all, but my wife will, so I know it is doing it fairly consistently.

Even though the truck runs fine and shifts well, it still has me concerned because it could be a sign of a transmission issue. The fluid is at the correct level (checked with warm/running engine, after driving, on a level surface). I swapped out the transmission shift solenoid pack a few months ago, due to a completely different (and much more severe) shifting issue, and it fixed that issue, so the fluid and filters are new. This little transmission bump has been happening for a week or two, so the last couple of months after changing the trans shift solenoid pack, it has not been acting this way.

Thanks so much for any input you can offer!