All Autopilot Trim is half-rate for 757/767
That is generally true but it "can" operate at full-rate when a multi-channel autoland is commenced!
Below from the Boeing 767 engineers training notes.
Autoflight Trim
FCC auto stabilizer trim signals are sent to one SAM. The control
and arm outputs that result use the same path as described under
manual electric trim.
If the pilot or FCC is not making a trim input, mach trim circuits in
the SAM will control trim operation using ADC inputs.
Trim rate in these modes is half of maximum as only one STCM is
controlling one hydraulic motor/brake combination.
Autoland mode with multi-channel engage of the autopilot can
operate at dual motor rate if required.
The condition that it "CAN" operate at full-rate is described below.
Multiple Channel FCC
During multiple channel operation, two or three FCC’s are engaged.
The FCC (first engaged) provides trim commands to its SAM,
immediately, when the elevator is deflected out of its neutral
position. The stabilizer moves at half rate speed.
If a failure occurs on the 767-300 that results in autoland 3 (three
FCC’s engaged) defaulting to autoland 2 (two FCC’s engaged), the
FCC not controlling trim engages the SAM not previously
performing the auto trim function. The two FCC’s command the two
SAM’s to trim simultaneously resulting in the stabilizer moving at
full rate (0.5°/sec). This full speed trim permits quick retrimming of
the airplane for go-around during a missed approach.