The 2-3 shift solenoid (SS) valve controls fluid flow
  acting on the 2-3 shift valves. The 2-3 SS valve
  is a normally open exhaust valve used with the 1-2 SS   valve
in order to allow for four different shift combinations.
If the powertrain control module (PCM) detects a non third gear ratio
  while third gear is commanded, then DTC P0757 sets. DTC P0757
  is a type C DTC. For California emissions vehicles and vehicles
  under 8,600 GVW, DTC P0757 is a type A DTC.
The numbers below refer to the step numbers on the diagnostic table.
Step 
 | Action 
 | Value(s) 
 | Yes 
 | No 
 | 
1 
 | Did you perform the Diagnostic System Check - Engine Controls? 
 | -- 
 | Go to 
Step 2
 
 | Go to 
Diagnostic System Check - Engine Controls 
 in Engine Controls - 6.0L 
 | 
2 
 | 
- Install a scan tool.
 
- Turn ON the ignition, with the engine OFF.
 
Important: Before clearing the DTCs, use the scan tool in order to record the 
 Freeze Frame and Failure Records. Using the Clear Info function erases the
  Freeze Frame and Failure Records from the PCM.
 - Record the Freeze Frame and Failure Records.
 
- Clear the DTCs.
 
- Select TFP switch A/B/C on the scan tool.
 
- With the engine running, apply the brake pedal and select each
  transmission range: D1, D2, D3, D4, N, R, and P.
 
Refer to 
Transmission Fluid Pressure Manual Valve Position Switch Logic 
. 
 
Does each selected transmission range match the scan tool TFP switch A/B/C display? 
 | -- 
 | Go to 
Step 3
 
 | Go to 
DTC P1810  
 | 
3
  
 | 
- Raise and support the drive axle assembly.
 
- Start the engine.
 
- With the transmission in the D4 range, use the scan tool in order
  to command 1st, 2nd, 3rd, and 4th gears while accelerating the vehicle.
 The vehicle may need to be road tested.
 
 
 Was 3rd  gear commanded and not achieved, or 4th gear commanded and   another gear occurred? 
 | -- 
 | Go to 
Step 4
 
 | Go to Diagnostic Aids 
 | 
 4 
 | 
- Inspect the transmission for the following conditions:
 
| •  | 2-3 shift solenoid mechanically stuck OFF |  
  
| •  | 2-3 shift valve stuck in the released position |  
  
| •  | Damaged 2-3 shift solenoid seals |  
  
- Repair the circuit as necessary.
 
 
Did you complete the repair? 
 | -- 
 | Go to 
Step 5
 
 | -- 
 | 
5 
 | Perform the following procedure in order to verify the repair: 
- Select DTC.
 
- Select Clear Info.
 
- Operate the vehicle under the following conditions, only if traffic
  conditions permit:
 
| •  | The PCM must see the proper gear ratio for each gear for greater
  than one second in D1, D2, D3, and D4. |  
  
| •  | Accelerate the vehicle with the throttle angle greater than 7 percent
  up to 89 km/h (55 mph). The TCC must be locked in FOURTH gear. |  
  
- Select Specific DTC.
 
- Enter DTC P0757.
 
 
Has the test run and passed? 
 | -- 
 | Go to 
Step 6
 
 | Go to 
Step 2
 
 | 
6 
 | With the scan tool, observe the stored information, capture info and DTC info. 
Does the scan tool display any DTCs that you have not diagnosed? 
 | -- 
 | Go to 
Diagnostic Trouble Code (DTC) List 
 in Engine Controls - 6.0L 
 | System OK 
 |