Stay away from the LS6 cam - it bleeds off low RPM torque with its late intake valve closing. It's more intended as a high RPM cam in light-weight vehicles, like Vettes. With your 3-ton beast, you need a cam that closes the intake valve early (like the LQ4 cam), but has more duration and lift. I would recommend the following two cams. Either would boost low-RPM torque and rev to about 5500.

Comp XR259HR 206/212 .515/.522 112

Crane 1449531 208/216 .530/.530 113 (Grind# HR-208/312-2S-13.53)