So I am getting a harsh/hard shift in 3rd ONLY, and it is extremely intermittent. Did it once last Sunday, then it was fine. Started again yesterday, but fine this morning. I have done the PCS due to the P1811 (at least 1 year ago). This is different. When it was happening Sunday, it did it both when the trans was hot, and cold. I also took care of the LF trans mount on the front subframe (6 months ago maybe), and the trans finally felt good when shifting. So much for that I guess. Anyone else have this?

No comments......???

Have you checked if has set any new codes since this new problem? Could be a sticky valve or the 3-4 shift solenoid might be giving up. How many miles since your last service? You might try and servicing it and adding some seafoam and see if that will help it, ya know mechanic in a bottle!

I would do a pan drop oil/filter change and look for anything out of the ordinary in the pan.

And the idea about the Seafoam is a good one. Throw some into the transmission about a week before you do the oil/filter change.