Hello I have an 11 6.7. Deleted with an ez link and 207,000 miles. I have the 6R140 transmission and as far as I know it is the original trans. Iv been having issues for a while with flared shifts and very firm shifts. As of recently it has gotten much worse. Usually the first time driving for the day the trans will try to shift from 3rd to 4th and it will rev up and act like its in neutral for about 5 seconds.
Other times the upshifts 1-4 and downshifts 1-4 are randomly shifting so hard that it makes your brain hit the inside of your skull! I have tried different tunes and no change. A few years ago I replaced a few of the shift solenoids and changed the fluid and filter and that helped for a few months but it came back. Iv read that people put an upgraded valve body in the trans and that solves it. Im also wondering if there could be internal damage to the trans and a valve body not help my problem. I have also heard that having deleted and tunes can cause a new valve body to not work correctly. Any recommendations would be greatly appreciated!