Last year Fiat-Chrysler Automotive appeared to have a runaway hit on its hands with the 2015 Ram 1500 EcoDiesel, offering 420 lb-ft of torque and nearly 30 highway mpg. Orders came pouring in from across the country, compelling Chrysler to double its sales target for the EcoDeisel engine from 10-percenet to 20-percent. After solving production bottlenecks at its Italian and Mexican factories, FCA seemed all set to start meeting customer demand with diesel-powered pickups.

But as WardsAuto reports, there seems to be a pretty hefty disconnect between actual EcoDiesel sales, and the number of vehicles Ram is producing. The latest numbers show that while the Ram 1500 EcoDiesel makes up about 12-percent of the retail fleet mix, production is closer to 18-percent. That’s a 50-percent difference between demand and production, representing thousands of potentially unsold trucks. What’s going on here?

If you look into vehicle registrations, the numbers are even worse, with just 9-percent of retail buyers purchasing a Ram 1500 with the 3.0-liter EcoDiesel V6. Many dealerships with dozens of Ram pickups in stock have just a handful of diesels on the lot, and the extra cost of the EcoDiesel engine is hard to sell at a time when gas prices seem to have settled down (however temporarily). At $4,770 more than the base V6 and $1,000 more than the popular HEMI V8, and with gas prices under $3 a gallon in most places, it seems like the EcoDiesel V6 is stumbling when it should be hitting its stride.

But if there’s anything we’ve learned in the past decade, it’s that low gas prices rarely last long. As long as FCA decides to stick it out and keep the EcoDiesel engine option, it should pay off in the long run.