You are correct! I am NOT a 4T65E transmission expert BUT I do have over 30 years experiencing working on my own cars, and no I do not mean tuneups. Transgo, on the other hand, has more experience with transmissions than most folks on the forum. I went back and looked at the Transgo shift kit instructions for the benefit of us novices and refreshed my knowledge on this whole hard shift issue (my temporary fix has lasted 5 years and 70,000 miles now) as to why their shift kit works to correct this hard shift issue. Changing fluid/filter often will do nothing to alleviate a hard shift issue most of the time!
Essentially what is happening with a hard shift condition is that as the springs/shims in the accumulator get mileage on them as well as the trans itself, the springs lose tension (become softer) which extends the time between shifts. When the computer detects longer shift times either from the accumulator springs losing tension or other issues in the transmission that occur with age/mileage, the computer tells the PCS to up the line pressure which is trying to reduce the shift times between shifts with higher line pressure-Thus the trans begins to shift harsher. The trans fluid temperature component of this issue is that very high trans fluid temperature will make the accumulator springs even softer (or just aggregate other issues in the trans with age/mileage) which is why high trans fluid temperature often triggers the hard shift condition-thus where the trans coolers come in.
The following quotes are directly from the Transgo shift kit instructions:
" With 70,000 miles or more miles on the 4T65E transmissions, they often need some hard parts"-mine had 88,000 miles when the first hard shift condition existed.
"Long Shifts make a 1811 code with default to hard or missing shifts. A scan tool will show long shift adapt time. This kit will shorten the shifts without making them rough" This is true!
"EPC (PCS) solenoid-This solenoid fails with no metal contamination even on a perfectly clean low mileage transmission" Thus my comments and my personal experience that changing the fluid/filter often will not prevent this failure.
"EPC (Pressure Control Solenoid)-P1811 or PO741 and other codes and failures are most often caused by a sticking armature in the EPC solenoid" This is an electronic issues and has nothing to do with the fluid.
Hope that this helps and addressed the naysayers.
