Yeah my friend drives an auto 4.3L blazer I think it's a 92 and it won't stay in park... anyways it started rolling back into traffic one day and I saved the blazer from getting smashed by jumping on the brake... He says the park pin is worn down too much.. What do you guys say?

 

could be the shift linkage needs to be adjusted.

 

I would have to say adjust the linkage if its got it.
If its cable then replace the cable due to there is no adjustment for cable shift.
(unless its an aftermarket shifter like a Hurst)

Its rare for the park rod to be wore, and if that is shot then you're looking at a trany rebuild or replacement.