My 92 GA 3300 Strange problem

I have a 92 ga v6 3.3 l with almost 195 000 km on it
sometimes, more often since a couple of week it does a strange probleme

This problem happen when on Park

-All doors get locked
-the light of the 'P' on the transmission get shut down or darker
-My RPM goes between 500 and 1100 RPM like...
500 a second later 1000 rpm, a second later
500 ..........
he could do this for a couple of minute
when my engine is cold instead of going between 500 and 1000 RPM it goes to 900rpm (instead of 1100 when the engine is warming up)

When i press the light who shutdown (or goes darker) sometimes the light goes 'ON' and everything go back like normal :evillol:
but sometimes the light does not goes 'ON' and the trouble continue :(

if i press harder on the light, the car dies :swear:

anyone got an idea of what is doing this ?

thanks

What do U mean by pressing the light?????????

on the transmission there is a light right to each letter
P *
R *
N *
D *
2 *
1 *

the stars represents the light, the light is on when the transmission is on that gear
when on park the light right to the 'P' is ON
when the trouble start this light goes off or darker

tanks

To answer your question the problem your having is that the shift module is shorting. I replaced mine costed about Total: $45.03 I bought it new from gmpartsdirect.com the part number is #22582545 INDICATOR

Is this hard to change
if not, how ?

thanks