You are completely correct
You are completely correct that production limitations are keeping both the Tacoma and Colorado sales where they are. However, I have seen multiple reports that the Chevy Wentzville plant is already at three full shifts and has been for more than four months. Link below. Sorry I can't make it live. You have to cut and paste. http://www.autonews.com/article/20150525/OEM01/305259968/gm-wrings-more-pickups-out-of-busy-plant
My prediction of the Colorado Diesel is it will sell strongly initially and settle at less than 20% of customer take rate after 6 months. Customers will do the math when diesel prices are high (winter) and realize the cost per mile is higher than other Colorados.