C4 won't stay in Park?

[fastsvo]

I am about to start my fresh 289/c4 combo in a '67 Mustang. Though the
shifer seems to be a little off as per the shift selector light in the
center console, it seems the transmission doesn't lock in place when in
Park. How do I know this without driving it? When in P, we can move the car
back and forth without resistance. This worries me. The shifter slides too
easily from R to N, I kinda have to slowly put it in R and feel for the
click, then N. How do I fix this? Thanks in advance.

-Eric