Seems like their might be a bug with the basic autopilot mode trim function. It is very very slow to change pitch or roll attitude in basic autopilot mode. Supposed to be around 0.5 degrees/sec for pitch and 2 degrees/sec for roll.
To quote the NATOPS manual:
"The basic autopilot (heading hold) is engaged by selecting the A/P pushbutton (at
which time pilot relief options appear on the UFC) then selecting the ON/OFF push button......At this time the aircraft maintains the existing pitch attitude. If roll attitude is less than or equal to
±5° at engagement, the magnetic heading is maintained. If roll attitude at time of engagement is
greater than ±5°, the roll attitude is maintained. The pitch attitude hold reference can be changed with pitch CSS to any value between ±45° pitch. The pitch attitude reference can also be changed with the trim switch on the control stick at a rate of 0.5°/second. The roll attitude hold reference (if roll is greater than ±5°) can be changed with roll CSS to any value between 5° and 70° of roll. The roll attitude reference can also be changed using the trim switch on the stick at a rate of 2°/ second."