Please note that it is simply mathematically impossible to build a perfect pitch shifter or time stretcher. There are a few commercial ones that work surprisingly well despite these physical limitations, but it will never be perfect. Autotune may for example work well with vocals but I have doubts it would get the job done for kicks and stabs. You can give
Rubberband a try (which is free, but not compatible with OpenMPT's license so we don't use it), but I can tell you that both "classic" ways of implementing pitch shifting and time stretching (namely resynthesizing the frequency spectrum with fast fourier transformation, and temporal overlapping of small snippets of audio, both used by the pitch shifter and time stretcher in OpenMPT respectively) do not handle drums very well. It's just in the nature of time stretching to smear transients.
What may be more helpful in your specific case is editing the samples by hand, e.g. to apply a fadeout to make a kick shorter, or delete small bits of it, or copy&paste bits to make it sound longer. I personally would never use a time stretcher for that.