I agree with Dobly, all this is covered in a lot of detail in the manual. Takes some fussing around but its there. And once you choose or create a kit that you want as your default, save it over Kit 000 and then it will be the one you get to start with each time.
Pads not triggering or cutting out quickly can be a mechanical thing (loose or broken wire, foam cone or cylinder fallen over) or it could be software (too high threshold, too low sensitivity, xtalk, mute groups and priority.. you could have a cymbal or the kick drum with high priority (sorry, forget if that's the exact term) but could be something is overpowering the pad you're finding cuts out or doesn't trigger)).
We usually test the theories by swapping cables, changing which input the problem pad/cymbal is in to see if it happens with other inputs or voices. Got to eliminate a few variables to find out where the problem is (of course, taking the head off and checking for broken wires etc is a pretty quick way to at least eliminate physical damage as the culprit).