For a 2003 Taurus SES. 12V 3.0 V6, Auto O/D.

Symptoms: when accelerating- for instance, freeway on ramp, passing, or pulling steep hills, car doesn't want to downshift on part throttle. Somewhere between 3/4 and full throttle, the transmission (or ECM) DECIDES "OH HOLY CRAP, MORE POWER SCOTTIE!!!" It then downshifts HARD to 2nd, bucks, chugs, hesitates, and generally misbehaves. Does everything but actually move forwards at a faster pace.

When you back off tbe throttle, it'll shift back up to OD andd resume it's normal pace. Pretty unnerving if you pull out to pass on a two lane road- hard to guess what to expect. Oddly, in normal in-town or freeway driving, it shifts up and down normally without any odd noises or other bad habits. No check engine light or any other warning lights come on.

Any ideas?

Looks like checking codes and looking at line pressures first

SHIFT CONCERNS: FEEL — HARSH


Possible Component Reference/Action
214 — ELECTRICAL ROUTINE
Powertrain Control System
Electrical Inputs/Outputs, Vehicle Wiring Harnesses, Powertrain Control Module (PCM), EPC Solenoid, MAF, TP, OSS, ECT, IAT, PSP, TFT, Digital TR Sensor, Internal Wire Harness and Shift Solenoid No. 3 (SSC), A/C
Run On-Board Diagnostic. Refer to Powertrain Control/Emissions Diagnosis (PC/ED) manual for diagnosis. GO to Pinpoint Test A, GO to Pinpoint Test B, GO to Pinpoint Test D and GO to Pinpoint Test E. For additional information, refer to Pinpoint Tests — Non OSC Equipped Vehicles in this section.

314 — HYDRAULIC/MECHANICAL ROUTINE
Fluid
Incorrect level
Adjust fluid to correct level.

Incorrect Pressures
High line pressure
Check pressures at line and EPC taps. Carry out Line Pressure Test. For additional information, refer to Special Testing Procedures in this section. See the Line Pressure Chart for specifications. If pressures are high or all shifts are harsh, go to Main Control Valve Body.

High EPC pressure
If pressures are OK and a specific shift is harsh. See the appropriate shift routine in the following chart:
Shift 1-2, Routine 232/332
Shift 2-3, Routine 233/333
Shift 3-4, Routine 234/334
Shift 4-3, Routine 235/335
Shift 3-2, Routine 236/336
Shift 2-1, Routine 237/337

Main Control Valve Body
Bolts out of torque specification
Tighten bolts to specification.

Gaskets and Separator Plate — damaged, off location
Inspect for damage. Replace as required.

2-3 Capacity Modulator Valve, Main Regulator Valve, Line Modulator Valve, 3-2 Timing Valve, Springs, Clips, Check Balls — stuck, damaged
Inspect. Repair as required.

Pump Assembly
Bolts out of torque specification
Tighten bolts to specification.

Gaskets and Separator — damaged, off location
Inspect for damage. Replace as required

EPC Solenoid — stuck, damaged
Inspect for damage and contamination. Repair as required. Activate solenoid using Transmission Tester. If solenoid operation cannot be felt when placing hand on solenoid, replace solenoid. Inspect O-rings for damage. Repair as required.

Thanks Vince. Made an appt. Wednesday to have it looked at. FWIW, baby bear drove it today in D instead of OD and it shifted flawlessly up and down.

Yeah, looks like the problem is localized to the valve body. Whether it be solenoid, valving, or electrical.