My truck has never been what I would call "smooth" shifting, coming from a Ram with the ZF 8-speed. This truck has always shifted rough(est) on the 3-4 shift, worst when the transmission is cold. I had really hard shifting issues about a month ago twice in two days, and now it suddenly did it again yesterday afternoon: the truck acts like when it tries to shift from 3rd to 4th it misses, slams back into 3rd, revs for a second and jumps to 5th. I've seen people also saying this can be caused by low transmission fluid levels, and can cause the transmission to fail if it goes long enough. Interestingly the ex-wife had a 2011 Jeep Grand Cherokee with the 5-speed Mercedes transmission that would do the same thing when trying to shift into 2nd. In that case it was failed valve seals letting fluid past in the transmission- it couldn't engage 2nd, would drop back to 1st hard, then rev and jump to 3rd. The dealership ended up having to replace the entire transmission. I'm going to swing by the dealership later and see what they can tell me.