Our 2006 GS300 has only 126k miles on it... lately, the car has been very sluggish accelerating between 20-30 mph. It's absolutely fine after that, but when entering a freeway or going about downtown, it behaves like this.

The other day I noted that at lights it would idle around 700 RPM; upon acceleration (and very gentle at that), it would suddenly pop to about 1700 RPM, and then suddenly drop to about 900.

I have a Blue Driver OBD tool (updated with latest firmware and running the latest app version) and it detected code P2757 with the following explanation:
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This MAY indicate one or more of the following:
• Lockup clutch has failed
• Shift solenoid valve SLU is stuck in "open" or "closed" position
• Transmission has internal problems
• Valve body is blocked up or stuck

Frequently Reported Fix
• Replaced Torque Converter Clutch (TCC) Solenoid Valve

Other Reported Fix
• Replaced Torque Converter Clutch (TCC) Solenoid
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Has anyone else encountered this code? if so, what did you have to do?
Do I still need to take it in for confirmation of what I have already found, and how much should that cost?
What danger do I face waiting to fix it? (we use the car very little, maybe 2K miles per year, and will take it with us when we relocate out of state and use it as a trade-in within the next 8 months or so...)

Also, should I think the car has magically gotten better because this problem seems to have not surfaced in the two days since I ran the Code Scan?

Thanks!