possible shift linkage problem
 

I'm having some problems where my shifter keeps popping out of the upper portions of the h-pattern (1, 3, 5, reverse.) Came out of reverse 3 times in a row to back up at a gas station the other day.

After looking at these sites,
http://www.gmhightechperformance.com...ild/index.html
and
http://www.noid.org/~lj/T56/T56.htm

I'm starting to think my problem is in the shift linkage. Are there any sites that further explain how the shift linkage works? What prevents it from being in two gears at once? (1st and 3rd or 4th, or 2nd and 3rd or 4th, etc..) I'm thinking it's not a bent fork because then I'd have 3 forks go bad at the same time?

Anyway, any help is appreciated... if you have pics further explaining please share.