[JL8Jeff]

Doesn't sound like an issue with the trans. Did you check the u-joints, driveshaft play, pull the driveshaft and spin the rear to see if the brakes are grabbing unevenly. See if you can have someone follow you on the highway and watch your rear wheels at 70 mph to see if there is any wobble at all. Are the rotors/wheels seating themself all the way on the axle flange? If there is any rust buildup on the flange the rotors might not seat all the way making it uneven. Definitely try swapping wheels/tires with someone if possible to help eliminate wheel/tire/balancing without spending too much time or money.