I came across this section in the user manual. Is this speed restriction on non-freeways/highways also the case in model S/X?
Autosteer is intended for use only by a fully attentive driver on freeways and highways where access is limited by entry and exit ramps. If you choose to use Autosteer on residential roads, a road without a center divider, or a road where access is not limited, Autosteer may limit the maximum allowed cruising speed. The maximum allowed cruising speed on such roads is calculated based on the detected speed limit including a Speed Assist offset of up to +5 mph (10 km/h). Any Speed Assist offset above +5 mph (10 km/h) is rounded down to +5 mph (10 km/h). However, you may select a more restrictive cruising speed by reducing the offset from speed limit setting (see Controlling Speed Assist on page 78) or by tapping the plus (+) or minus (-) buttons on the touchscreen.