Howdy Ralph,
I'm sure others will have tips as well. One thing that I've found that helps in the realistic sound is to actually skip a hit here and there for the really fast rolls. This can be accomplished either by (1) manually entering the notes first (eg. using a mouse) and then deleting some here and there, or (2) more convincingly, by recording the roll "live" using two fingers on two keys of your MIDI keyboard. You can record to two different staves (as if you were recording a two-hand piano piece), adjust the pitches of the notes in the one staff to match the other staff (to get the pitch correct for the timpani) and then merge the two staves into a single staff. If you don't think you can record it at tempo, then you can change the tempo while recording to something really slow so you are comfortable with the roll, and then speed up the performance when you're done recording.
Have fun
Sherry