Mazda 6 Service Manual: No.9 abnormal shifting

No.8 does not shift to fourth gear (4gr)

No.10 frequent shifting

Other materials:

Mazda 6 Service Manual: Intermittent concern troubleshooting
  Vibration Method 1. If malfunction occurs or becomes worse while driving on a rough road or when engine is vibrating, perform the steps below. Note There are several reasons vehicle or engine vibration could cause an electrical malfunction. Some of the things to check for are: ...

Mazda 6 Service Manual: Joint shaft disassembly/assembly
1. Disassemble in the order indicated in the table. 2. Assemble in the reverse order of disassembly. Joint Shaft Disassembly Note Disassemble the joint shaft. Bearing Disassembly Note Remove the bearing using the SSTs. Dust Seal (Right) Assembly Note 1. Apply grease to the new dust se ...