The black tranny, unless it's had a forward only conversion kit installed, will do exactly what's shown in your video. The For/Rev gears have a small clutch that disengages at low RPM so it can shift gears.
Try taking an air nozzle and blowing the across spur gear to spin it up really fast. The truck should jerk once it gets enough speed. I personally eliminated reverse because I couldn't stand the annoying bucking when the truck took off.
Installing the FOC makes the black tranny pretty much bullet proof, unless you put a .21 in the truck, then you're more likely to twist driveshafts, not break the tranny.