Set constant length warp mode
Multi-select all slices and set the "WarP" parameter to "Ln.C.M".
This mode ensures slice time is automatically varied so that it perfectly stretches the playback over the duration of the step length("Ln") as determined by the song's BPM, and keeps the pitch constant ("C"). The difference from the "Ln.C.S" mode, is that the slice's playback speed is scaled in proportion to (e.g. in context of) the full master ("M") sample length.
Try auditioning the slices after you have set their "WarP" parameter. If your auditioning length (hold write + turn value knob) is still set to 1 (default), you should hear short bursts as the slices are "crammed into" one step's worth of time. Set the auditioning length to 16 (e.g. one bar, which is the natural length of the Amen drumloop) however, and you will hear the drumloop play at a more normal speed. Set the auditioning length to 32 and you should hear the drumloop play at half the speed (e.g. the sample is stretched over 32 steps at your chosen song BPM). You will also start hearing the quintessential "metallic" artifacts that the oldschool samplers were known and - depending on who you ask - celebrated for. Many Jungle and Drum and Bass tracks rely on these artifacts to impart further interest and energy on their breaks. As you will see, you can summon these artifacts on demand once it is time to build you new break in the sequencer.
As a side note, it is worth mentioning that you can also use the "Ln.V.M" mode, which does not apply the pitch correction at all and instead modifies the pitch of the sample to accommodate the time it needs to cover. This would have been the go-to technique to sync non-sliced sampled drumloops with different BPMs before time stretching was available.