What is "hard acceleration" for you? Is it wide open throttle? If it is shifting like this at 3K rpm, then maybe that's not the problem. Hold it in 3rd while accelerating to around 3k rpm then shift to "D" and see how the 3-4 shift feels (don't let up on the throttle). In my case, I did think that it was doing it even at harder acceleration but I think that it was shifting prematurely, because when I made the adjustment it went away. What I felt was a slight shudder, almost like running over 2 rub strips on the highway. If you do the adjustment, count the number of "flats" or sides of the adjusting nut. I had to go almost 2 complete turns before I felt the difference. If you go the wrong way, you will know right away because the shifting will get even harder at the lower shift point. Just remember to keep track of the adjustment...
1993 300e-2.8 - gone now <sigh>
"Do not adjust your mind, it's reality that's malfunctioning"