I have had this 1/2 shift problem for the last nine years. The 1/2 shift seems slow then finishes with a bang or bump. The trans shop referred to this as "slide bump". This occurs when starting out with the shift lever in D position. If I start out with the shift lever in 2 position, the 1/2 shift is quick and fine. I noticed this rough 1/2 shift when I got the truck @39,000 miles. At 62,000 I had enough and took it to a trans shop. They said a rebuild would fix this. After four months of trying different clutch materials, different valve bodies, additives, and lightening my wallet by $1,000 they said this was the best they could do. I needed the truck so I just took it rebuilt trans, rebuilt converter, but still the same old problem. I now have 82,000 miles and it is still the same.
I have my own theory on this and wondered what others thought. The second gear has what is called a sprag which is a one direction clutch. When in Drive and it is time for the 1/2 shift the clutch grabs the sprag and finishes the shift by powering the second gear set through the sprag. When the shift lever is in the 2 position the sprag is locked up and not used so that you don't have free wheeling and have the second gear as an engine brake. My question is could this sprag be worn and slipping and then grab with a bang.
Any thoughts on this would be appreciated.