As mentioned, applying the brake a bit might get it to drive both tires. Mine seems to work fine, but I don't really test it much. I use the 4WD if its slippery. Sounds like you could use a locker.
Using the emergency brake on the '03 and up Trac-rite is recommendation in my Dodge truck owners manual.
As was mentioned the wheels on Trac-rite has to be rolling a bit. I've been stuck more than once with one wheel with traction and the other on ice/mud/green grass and no forward motion. I know when the new 3rd gen '03 Dodges first hit the street I was a member of three Dodge/Cummins forums and boy the first year lots of off road members were cussing the new AAM Trac-Rites.......however its great for leaving two long black marks on the dry pavement.
