I've recently tried to upgrade from an old toshiba laptop running mach3 on an old mill to a newer dell type and have found with the same settings that the 3 axis are jumping and running rough, could it be that the digital drives need to be retuned, if I reconect the old laptop it runs smooth again.
didn't want to go messing with the drive settings as with the old laptop it runs well.
Old laptop is giving trouble, sometimes wont start and a bit hangy.
I've tried to measure the voltage on the printer port and both seem about 4vdc.

Laptops are not supported for use with mach3, because a lot of them won't work.

You can try disabling all the laptop power management features in firmware and operating system, it may help but it might not,   

 - Nick