It's interesting, after thinking about this, my '15 6.4 gasser with 66RFE kept pushing the trans dipstick out. The first time I found it was right after I had it in for and engine oil change, so I chalked it up to a careless tech checking around. But it kept happening. I ended up replacing the dipstick, and it did "seem" to stop it. Now I wonder.
In 88 we ordered and bought a new GM short bed, stepside for my wife. About 2 months after taking delivery we got a package in the mail. GM sent us a locking dipstick ( over center handle with a rubber expansion plug) for the trans. It seems that a hot trans would lift the stick and puke out the tube.