A power train for a machine is provided having a power source and a transmission, which includes a plurality of gears configured to produce multiple output ratios when selectively engaged. The power train also has a torque converter operatively coupling the power source and the transmission. A lockup clutch is associated with the torque converter, and the engagement of the lockup clutch is restricted so that the lockup clutch is engaged only when permissible gear ratios are actuated. The power train further has a controller in communication with the lockup clutch, the controller being configured to selectively engage the lockup clutch in either a first or a second shift mode with the number of permissible gear ratios being greater in the first shift mode than the second shift mode.