'94 GCL O/D problems

My tranny grinds and pops when it shifts into 4th(O/D) and bangs when it try's to downshift out of it. When I have the shifter in first or second, I have NO problems. only when I shift into the D (O/D) selection that this problem occurs. I read on another forum that these jeeps are supposed to have trouble codes for the tranny, that flash via the O/D selector switch on the dash. Supposed to be 15 different possible codes. It is supposed to show the codes when you do the on of on of on thing with the ignition, just like checking the Emission fault codes, but I didn't see anything flash on the O/D switch. Anyone got any clues?

Open oil pan and check. As early as better.

BR,
Arkadiy