The 3-4/4-3 speed depends on your exact calibration, but in general it's around 35 MPH for 3-4, and 32ish for the 4-3.
The reason you feel that lag in the 4-3 is because the forward clutch comes back on before the OD band has finished completely releasing.
The reason you feel that lag in the 4-3 is because the forward clutch comes back on before the OD band has finished completely releasing.