Many forum users on different Honda forums were trying to explain grade logic up-shift/downshift control using copy and paste method without being able to answer the question HOW the smart ass Honda ECU determines that car is on incline vs flat road.
They even listed some inputs the ECU used to figure out the incline gradient such as wheel speed sensors and barometric pressure
Here is the answer (thanks to soiled torn copy of repair manual I got for free)
The healthy car is allowed to decelerate on test road from initial speed A to final speed B with closed throttle and it takes 20 seconds; the time is written and loaded into the ECU for normal downshift sequence
Next, the test is repeated for but the car goes downhill and it takes 30 seconds to go from speed A to speed B (the car slowed down LESS in first 20 seconds)
In this case the different downshift sequence is programmed into ECU, so the less speed is lost in certain time the more aggressive downshift schedule will be selected by car's ECU. Some other factors such as engine temperature, application of brakes, electrical load and different AT mode will be used as correction factors.
SO the low engine drag (low restriction intake and exhaust, long valve overlap and low compression) will fool the computer and aggressive downshifting may take place.
According to the graph from the book, when gas pedal is FULLY released at 50 mph [green line] with no brakes are applied on the flat road, the car will shift from 5th to 4th at about 31 mph,[blue arrow] then go from 4th to First at ~10 mph [red arrow]





So the car will not slam from second to 1st , it slams from 4 th to first with torque converter (TC) clutch applied!!
The TC clutch is released in P but APPLIED in N!!!
In addition, Fit has two stage lock up mode which makes things even more complex
PS I missed 4 speed manual!!