Just goes to show that the Seafoam does work but I don't think it should be left in the tranny for any extended period of time. It is not an ATF conditioner.
On this particular LeSabre the first pan drop service with new Dexron III ATF and screen filter was done around 70K miles. Then around 125K miles when we had Cottman's replace the PCS solenoid. However, at around 135K miles the hard shifts and the P1811 DTC (max adapt, long shift) returned.
The LeSabre was one of my test vehicles, a total of 3 GM cars with the 4T65E autotransaxle in which I ran a GM Tech II scan tool and found the shift timing was out of specs...greater than .65 seconds causing the P1811 DTC to set and commanding high line pressure (max) and as a result the hard upshifts and in some the whining sound. This is to be expected due to tranny fair wear and tear and clutch pack material wearing away.
What we did was add the Seafoam to clean it out. Ran it for a couple of weeks and then did a pan drop with a new Filtran screen filter. The AC Delco TF304 screen filter is identical by the way and in reality a Filtran brand in Delco packaging. Then I added a a shift kit which was installed in the 1-2, 2-3 accumulator which can be accessed from underneath. Topped it all off with the new Dexron VI. Used the Wallyworld Supertech brand Dexron VI for $3.00 per quart since another fluid drain will be performed in about a month.
So far no problems to date and the shifting is excellent. Possibly a good work around for people having PCS issues or re-ocurring PCS issues. Time will tell.