The collisional loss of vibrational energy from polyatomic molecules in triplet electronic states has been studied in new detail through a variant of the competitive radiationless decay (CRD) method. Experimental transient absorption kinetics for T-1 pyrazine vapor in the presence of helium relaxer reveals the competition between unimolecular radiationless decay and collisional vibrational relaxation. These data have been simulated with Monte Carlo stochastic calculations equivalent to full master equation solutions that model the distribution of donor vibrational energies during relaxation. The simulations included energy-dependent processes of T-1 --> S-0 radiationless decay, T-n <-- T-1 optical absorption, and collisional energy loss. The simulation results confirm earlier findings of energy loss tendencies that increase strongly for pyrazine vibrational energies above similar to 2000 cm(-1). It is also found that the experimental data are not accurately simulated over a range of relaxer pressures if a simple exponential step-size distribution function is used to model collisional energy changes. Improved simulations are obtained by including an additional, low-probability channel representing large energy changes. This second channel would represent "supercollisions," which have not previously been recognized in the vibrational relaxation of triplet state polyatomics.