Overdrive light on gear selector blinking

The transmission in my 1996 F250 keeps going into "safe" mode as indicated by the hard shfts and the overdrive light on the gear selector blinking. I've been told this could indicated a transmission about to fail or a NSS giving a false code to the ECU.
It seems that this started right after the truck was ran on the dyno for a smog check. I know they plug into the OBDII connector to check all the related systems. I'm wondering if I'm doing damage to the transmission number one and if the "safe" mode is a reaction to something that was tweaked when they plugged in to the OBDII connector?
I'd like to be a little more educated before I let it go to the transmission shop.
Any help and/or guidance ia appreciated!!
Thanx, Mike

Plugging in to data link wont cause that. Most common problems are VSS and MLPL manual lever position sensor. Need to have some pull the codes. I hav a 97 ere now with flashing and the 2 gear one way clutch is broken.

Thanx for the heads up!
When it's in "normal" mode, the truck seems to run and shift properly.
I'll take it in and see what codes show up.
Thanx, Mike

The o/d light has never worked in my 92 and the trans has hard shifts sometimes so I am thinking some one removed the bulb,I have put about 175,000 miles on it this way with no problems. How does one pull the codes for the trans. Jeff