Mopar 557 cam

Opinions on cams will vary greatly and the exact performance opinion is just as wide. Your statement of lack of low end performance is understood. The cams you listed are a heavy street cam with not to much below there rated rpm range.
Not knowing the cam you have now...
Try a look at this cam instead. It is slightly smaller and will give more torque than the other cam. It has pretty good lift to take advantage of the ported heads.
Voodoo Solid Flat Tappet Cam - Chrysler 273-360 272/280 - Lunati Power