Let's talk Transmission Maintenance...

[Davidf]

Do it! Drain the fluid, replace the plug and start/run the engine for a few seconds. This will pump more fluid out of the clutch packs and torque converter...it wont hurt anything as there is plenty of residual oil to keep part lubricated. Use a suitable fluid such as Mercon SP, Pentosin ATF-1, or the OE ZF fluid. Personally, I choose the Mercon SP fluid as it was developed by Motorcraft/Ford specifically for the ZF6HP26 transmission as manufactured by Ford under license from ZF. Future change intervals should be 60k miles unless you use the OE fluid (then you can go longer). Don't let anyone scare you about crud being dislodged and blocking passages. Just do it. At 126k miles, I would be inclined to drop the valve body, replace the Mechatronic sleeve, install a Zip Kit, and replace the solenoids. Shift quality will be improved or future issue will be pushed way back.