Dice Roller, the special rule is on P38 of the "Barbarossa" supplement.
"When rolling for crossing difficult terrain and obstacles, a T34 may re-roll the D6 is it wishes. The Russian player may always take the lower of the two dice rolls".
As I guess this was to reflect the T34s better mobility compared to comparable German tanks in 1941 I'm not sure such a rule rolls over to later periods vs tanks such as the Panther, or when the T34 weighed more as the T34/85?
Regards.