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Welcome to Just Answer, I'm Chris (aka-Moose). I've been an independent contractor here for 13 years, and have gotten pretty good at diagnosis & repair sight unseen. However, I'm not good at sympathy through a keyboard. I do care about you, your vehicle's issues, and the funds you're spending, just not good at showing it. Sometimes I respond above your skill level, am to blunt or rough around the edges, just let me know so I can help you best to your and my ability. I am most often online central time 11-3 midday and 8-3 at night.
Once you get it into 3rd, does it shift normally?
Do you have a scan tool to see if the computer is commanding 3rd gear long before it actually shifts?
Will your scan tool allow you to see the PCM commanding shifts to occur?
You would go into the data logger section and look at the PIDS and find one for gear which should show something like 1-2-3-4
I noticed you have not responded. I assume you may be having trouble figuring out how to reply. I am going to try and answer now with the information you did give me. It will be brief and general for now, but I can do better once you respond.
If the computer is commanding this odd shift pattern then it could be the TP sensor. If it is commanding a shift but the shift is not occurring immediate then the transmission has internal issues.
Thanks for letting me assist you, Chris.