'86 Auto 4cyl.-Won't go into park

When I try to put it into park it won't stay in park but slips back into reverse. My shifter is on the column. All the indacator's are one off ie: its showing park, but its actually in reverse, showing reverse is actually in neutral, etc.
I replaced the spring and plastic (teflon) bushing down by the tranny. Any Ideas HELP it's an 86 pick-up GMC S-15. The truck still starts and I'm driving it.