For several years now, GM has dangled the promise of a mid-size, diesel-powered pickup in front of us, bringing back the Chevy Colorado and GMC Canyon nameplates to provide a vessel for the new 2.8 liter Duramax four-bangers. Both trucks were supposed to hit dealerships this past fall, but the massive emissions cheating scandal that engulf Volkswagen has brought closer scrutiny to all diesel-powered vehicles sold in America.

The Truth About Cars reached out to GM to find out what the holdup was, and the response from a GM spokesperson would only say that the trucks are still undergoing their “final validations” without going into specifics.

This final validation is different from the EPA’s emissions certification that GM already obtained, further raising eyebrows regarding the issue. Some would-be buyers placed an order for a Duramax-powered Colorado or Canyon dating back to August, only to be told that their trucks won’t be ready until mid-January at the absolute soonest. While GM technically still has a few days to shop its diesel pickups to meet its fall 2015 deadline, from the sounds of it they won’t make the grade.

While we understand this can be frustrating for customers who just want their trucks delivered, it is a far better thing to fix any potential problems at the factory before shipping them to buyers. The Chevy Colorado and GMC Canyon have already proven popular with buyers, but GM is hoping the diesel models can make the smaller trucks even more appealing to a wider audience. If the diesel models ship with major issues though, it could deal the deathblow to the new Duramax motor before it even gets a fair shake.

In other words, GM only has one chance to get this right.