I have the Sherman Hill route, and when the Gas Turbine was released, I thought I was going to be able to use it on the route. Unfortunately, that never happened. The turbine should have been part of the free DLCs DTG made a few years ago. Could we get the UP "Big Blow" Gas Turbine as a separate-sale DLC for Sherman Hill and the UP Wasatch Route?
Maybe release it as part of a Union Pacific Turbine pack, and include the 1st generation and 2nd generation "Veranda" turbines as well.
If you didn't get it with Sherman Hill, I think you can still email Dovetail Support and they'll give you a key for it. It's how all the TS Rewards stuff has worked so far if it didn't come in the download on Steam.
You should also supply an app manifest to show that what you are missing isn't in your steam library, and they will send you a code for the missing DLC. I did it with the Military flat cars, and got them within a few days, should also work with missing GTEL's DLC's for Sherman Hill too.
So looks like DTM's next project will the 1st and 2nd Gen UP turbines. So we will have all 3 turbines in the near future.