I have found those code to be shown in not only over boost conditions (wastegate) but EGR flow as well as Catalyst conditions.
Being that you are lacking power I suggest you check the EGR for being stuck open, or the catalyst for being clogged.
These engines do not like light driving, you should drive them hard from time to time to kep the catalysts clean of debris.
DTC Decoded P1251 Toyota Parts Blog
"More times than not, the problem that throws this code is with the turbo solenoid valve. "
Check that and clear the code to see if it comes back with same code
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