Not normal. If it physically kicks out of gear..as in you have to use the shifter to place it back into a position, either the linkage needs adjustment or there is a bent shifter fork in the transmission. If you are referring to the lack of engine brake, there may be a problem with the one-way bearing or belt. Both can easily be inspected. But know even at best, you will only have engine brake down to where the speed and engine idle RPMs cross which is about 5-7mph