Does the truck have the driveline with a short torque tube mated to the carrier bearing, and an open driveshaft behind the carrier? If so, it's possible for the seal at the front U joint to fail and allow transmission lube to run back to the carrier. The leak will be at the back of the transmission, not the center bearing. Check the lube level in the transmission- - - -it's probably low.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!