I need help on what to do with my 1995 Nissan Sentra SS Automatic Transmission (GA Engine)

The issue occurs when i put my car in reverse, when i am parking in a inclined surface, the reverse has no backward push and seems like in neutral, if it pushes backward its really weak. this happen also on uneven surface which cause me the other day push may car to get it parked.

D,1,2 and OD seems to be working properly, no jerk, or delay shifting. i just recently change my ATF Mobil ATF220, and upon checking the is fine and its not smell burnt.

Any idea guys what would be the cause of the issue?

Thanks in advance