Truck performance observed on grades on National Highway 7 in Argentina is described. The observed weight-to-power ratio distribution in Argentina is shown to be considerably higher than that in North America. Also, a speed prediction model based on the simple force balance equation is fitted to the field data. The model explains about 80 percent of the observed variation, and for steep upgrades the predictions are similar to values observed in the United States. Acceleration and deceleration performance curves are also given. Finally, a validation of the model is presented by comparing the predicted and the observed speed profiles along two upgrades for trucks of known weight-to-power ratios. The shapes of the speed profiles predicted by the model closely replicate the observed speed profiles.