nothing in the transmission will cause a vibration. its more than likely the axles or the tires.
umm ok?
i doubt its this but lockup on the torque converter happens between 45 and 50 normally.
99 Grand Prix old build- CAI, Custom exhaust, HV3, Stage 2 TB, custom tune, ported heads intense s1x cam, headers.
Nothing great Just a small T66 Turbo with a Hv3 On a stock tranny untill i finish the other one.