No high speed spin

Next suggestion is to run through the unit though an automatic test mode to see if it will go into the high speed spin. If it does run though without an error code that is telling us you can eliminate the motor, belt and bearing. We have had two circumstances where our technician replaced one board with out correcting the issue and then replacing the other two boards still having the same issue of slow spin. We then called the factory to see where to go next . They told us they have seen many circumstances when the new board that was replaced was a good, but damaged by one of the other two boards that were in the unit. We ordered all three boards and installed them at the same time and corrected the issue in both cases. We then sent the other boards back as defective parts.

Hello, I am Matt A factory certified technician from Ace Appliance. We have had many situations where the motor control and the main control board can not communicate. This is a common failure with these units and can cause high speed spin issues.
Unfortunately there are no diagnostics to determine which board has failed. You just have to replace one and see if it works.
As one board has already been replaced it is the other one that has failed.
You can run the diagnostics program if you like. System causes interference in the communication between the CCU (computer control unit) and the MCU (motor control unit).
Please see the information below to run the diagnostics program. I have also looked up both CCU & MCU so you have the parts breakdown and the part numbers for both boards. Please make sure after diagnostics you have no stored error codes. If you do please send them to us in this same thread link as we will stay with you on this issue until it is resolved.

DIAGNOSTIC TEST
There are two operation modes:
Indication of last four error states that have been recorded by the
appliance, indication of the SW versions, and implementation of
the automatic test program.
Starting Diagnostic Test only.
Starting Error History, Software Version, and
Diagnostic Test:
NOTE: Washer must be empty and the control must be in the
OFF state.
1. Close the door.
2. Select any one key (except “STOP/CANCEL” and “CONTROL
LOCK” [EOC]) and follow the steps below, using the same key:
Press/hold Release Press/hold Release Press/hold
for 2-5 for 2-5 for 2-5 for 2-5 for 2-5
seconds seconds seconds seconds seconds
3. Upon release, all yellow/green console LED lights will turn ON
for 5 sec.
4. If there are any failure codes stored by the washer, the display
shows them.
Note: The last four errors will be displayed.
5. Press the same key to advance to the next code.
6. After the indication of error codes, the UI, CCU, and MCU SW
version will be displayed.
7. The number of cycles since last clean washer cycle is displayed.
8. All green console LED lights will turn ON for 5 seconds.
9. Next the washer begins the automated diagnostic test.
10.To cancel out of service mode, press the “ST

HI. Here is what the F71 error code means on your washer.

USER INTERFACE HEARTBEAT FAILURE
If a Central Control Unit Heartbeat Failure is displayed,
no communication is detected from the User Interface
to the Central Control Unit.
Possible Causes/Procedure
1. Check for continuity of the User Interface harness.
2. Check wire harness connections to the User Interface
and the Central Control Unit.
3. If the drum is not rotating, unplug the MCU from the
CCU (the MI3 or M13 connector). If the code goes
away, then replace the MCU. If the code does not go
away, replace the CCU.
4. Replace User Interface if drum is rotating.

Since you have replaced the MCU your only two options would be the CCU or the User Interface. Follow the steps provided to find out which one is faulty. Let me know if you need any further assistance.