Originally Posted by repechage

Yes, but before that step... The threads on the new cartridge bottom bracket do not look clean in my book. They should be bright and shiny all the way down to the root of the thread valley, maybe there is grease in the thread valleys but I want to know it is only my grease, not grease and dirt. This also applies to the bottom bracket shell. Do that cleaning and see if it goes any farther in. If you still have resistance, then have the threads chased. Note though that the cartridge has more threads than the previous cup, spindle assembly, so the thread cutting and cleaning also has to be to the necessary depth.

Oh yes, try the new cups separately, before you try them as a left and right assembly. Bottom bracket shells are not always threaded concentric and parallel. The Campagnolo tool and some others will correct this as the two taps mate, some taps are without this feature.