07 GT Auto Trans. Issue. Any Ideas?

Hello! I own an 07 GT Convertible with an Automatic Transmission that I bought used 2 years ago with 36K miles. It now has just over 40K miles and has had a strange, intermittent problem since I've owned the car that is very annoying, and I can't seem to find anyone who can give me any advice. During aggressive driving under WOT when the trans is about to make it's 2-3 upshift, it hesitates to make the shift (like it doesn't know what to do) and will then skip 3rd gear and go directly into 4th gear. The other issue that I'm having is when just driving around normally with the OD turned on, when accelerating and going through all the upshifts, when in 4th gear it will skip 5th and go directly into OD. Is that normal? What I've been doing to help with that is to turn the OD off, and it will then make the 4-5 upshift and I can then engage the OD when I desire. My thinking is that there is an issue in the solenoids in the transmission valve body, but I'm not sure if this is something that can be corrected with a tune file (I have an SCT Tuner) or if the transmission is going to need to be repaired? Has anyone experienced anything similar, and what did you do to correct it? Thanks!

jpplaw said:

The 5R55s trans has 1st, 2nd, 3rd, 4th, & OD. The 5th gear is the OD. If you switch off the OD, your top gear is then 4th. You may be feeling what you think are extra gear changes in 4th and 5th but it is only the converter lock-up function.

With a 5R55s, never punch it WOT in OD. It will kick down to 3rd and wreak havoc with the tranny after a few times. Shut off the OD before any WOT runs.

These trans also have problems with the servo bores getting worn (steel servos riding cock-eyed in unsleeved aluminum bores - which is just a recipe for problems) which then leak internally. That can be a cause of shifting hesitation, especially with 3rd gear and OD. It takes some major surgery to correct and sleeve the bores. An aftermarket trans (Level 10 definitely does, and TCI & PA maybe) should come with the sleeving already done.

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Thank you for the informative response. Wasn't really the news I was hoping to hear though. I've been hesitant to take it in for service due to the fact that what will probably happen is that I'll be told that they cannot duplicate the problem. I've been down this route before with another vehicle (F350 with E40D Trans.) that had similar problems. I do have an extended warranty on my car that covers the transmission, just haven't been too keen on turning my car over to some service department. Maybe I should wait until it totally takes a crap, then they can't tell me that they can't find the problem!