The posts regarding spring replacement were from flared 2-3/3-4 shifts which usually happens at 1/2 to 2/3 throttle. I have noticed that at full throttle I would experience hard transmission shifts like you have. At 165K miles I would not rule out a worn spring. Once my spring arrives and I install it I can determine if it fixes the hard shifting at full throttle.

I am offering suggestions for you to consider before throwing in the towel and having your transmission rebuilt.

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Ray
1998 Mercedes E320, 200K Miles
2001 Acura 3.2TL, 178K Miles
1992 Chevy Astro, 205K Miles