Waiting for GM’s new inline-six diesel? Your patience is about to pay off.

Customers who are excited for a diesel engine to appear in GM’s half-ton 1500 series pickups shouldn’t have to wait much longer. According to the Order Guide for vehicles built by The General, the 3.0L inline-six turbodiesel was added to the books on March 11th.

Codenamed LM2, we don’t yet have official specs for this mill. Rumors abound that the engine will make somewhere in the neighborhood of 280 horsepower and 450lb.-ft of torque. For comparison, Ford’s 3.0L PowerStroke V6 makes 250/440 in the F-150 while Ram’s on-again off-again is-it-or-isn’t-it available EcoDiesel six-pot is good for 240/420.

According to the GM order books, the new Duramax will be available on a quartet of trims: mid-level LT, sporty RST, snazzy LTZ, and fancy-pants High Country. It’ll be a stand-alone option on the latter two, including a 220-amp alternator and engine block heater for yer money. The other pair of trims will also receive those extra bits of kit when the diesel engine is selected but RST customers will need to pop for the Convenience Package with or without bucket seats, the Z82 trailering package and a locking diff. Same goes for the LT, save for the buckets because that trim is only available with a bench.

The RST, shown above, is an example of a Silverado that’ll be available with the Duramax. It’ll be lashed to GM’s new 10-speed automatic and have a set of 3.23 gears stuffed into its rear end. Don’t look for the diesel on a regular cab Silverado, at least not at first.

Over at GMC, the diesel mill is going to be available on every trim except for the base truck. This includes the tasty new AT4, Denali, and even the oddball Elevation Double Cab.

Look for more details here at off-road.com when we learn output numbers and towing ratings for The General’s new half-ton diesel.