you want to look at your keystrokes for that effect.
I think the key parameters for a steel drum are dependent on how hard you hit the drum. For example, when you hit the drum hard, there is a pitch modulation of not just the note that was struck, but because the 'heads' are all interconnected... you will get harmonic ringing of the other note. Also, the harder you hit the drum, the more high frequency content there is in the sound.
Therefore, you will want to look at making a few parameters velocity sensitive such as cut off frequencies as well as pitch... and maybe make the pitch change more subtle if you think it is playing with the tuning too much. Regarding the tuning, you could also consider assigning an LFO to the pitch and playing with the rate of the LFO so that it does change slightly from note to note, but if you beat sync the LFO, then it should come right musically in the piece if you dig my meaning.