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  • Long-Term Report 3: 2018 GMC Sierra 2500HD Denali

Long-Term Report 3: 2018 GMC Sierra 2500HD Denali

Long Term Report 3 of 4

Jun 3, 2019
While we try our best to break up these reports by quarter and keep a relatively even number of miles in each one, sometimes it just doesn't work out. In the previous report we covered more than 7,000 miles, while in this one we hit just over 3,000. Regardless of that, we're still learning a lot about our 2018 Pickup Truck of the Year award-winning GMC 2500HD Denali.
As the previous report period closed and this new one began, the Sierra alerted us that is was time for not only another refill of exhaust fluid but also an oil change and fuel filter replacement. All of these service intervals are calculated by the truck's computer based on usage and we've found that we're hovering right around average. The typical oil change interval is 7,500 miles and fuel filter life should be about 15,000. Exhaust fluid is trickier, and while it should last about the same as an oil change we've found that the truck continues to consume the fluid at a rate of about seven gallons every 6,000 miles. If you frequently tow heavy loads, expect that number to go down. Fuel economy is averaging around 14.5 mpg, though that doesn't vary whether empty or loaded with a 10,000-pound trailer.
Photo 2/5   |   Long Term Report 3 2018 Gmc Sierra 2500hd Denali 001
Speaking of towing a 10,000-pound trailer, we did just that. Our 2002 Silverado 2500 project needed to be hauled around while parts were being installed, so we called upon the Sierra to handle the task. Even with a tongue-heavy load, the GMC handled the haul with poise and composure. The integrated trailer brake controller helped slow the combination with ease, nearly stopping the entire setup with little use of the service brakes. With Tow/Haul mode active, the truck's digital instrument display brings forward useful information such as transmission temperature and trailer brake gain. Also, while in Tow/Haul mode, the response from tapping the directional indicator stalk switches from three flashes to six, allowing more time to change lanes with a trailer in tow. It's the little touches like these that make towing with the Sierra less of a chore and more of a joy.
Photo 3/5   |   We'd like to use the analogy of our time with the Sierra being like a roller coaster, but in reality it has been exactly the opposite. Living with this truck has been nothing short of smooth sailing.
In our time hauling the project Silverado around we got to chat with many industry experts about our likes and dislikes with the 2018 GMC Sierra 2500HD Denali and its L5P Duramax engine thus far. One of these guys, a shop owner who's been involved in working on Duramax engines for more than 20 years, described a driving characteristic of the truck that we'd noticed early on but struggled to convey. Driving the Sierra slowly on and off the throttle, for example when approaching a stop light or navigating a parking lot, feels a lot like riding a dirt bike with a heavy flywheel. In simpler terms, there's very little coast. The truck goes from accelerating to decelerating without much in-between, similar to driving an electric go-kart. We aren't ready to call it a bad thing, however it's unique to this L5P Duramax and Allison drivetrain combination, as we've not experienced it in the same way on other HD pickups.
Photo 4/5   |   Note the position of the fuel level indicator. We previously talked about this being perfectly linear. Well, now more than 15,000 miles later, it is not. In typical GM fashion, the first half goes slowly while dropping off sharply in the second half. From here, we probably only have 100 miles until empty.
Photo 5/5   |   One of the most noticeable telltale signs of an exhaust system regeneration occurring is an elevated idle speed. While normal is about 600 rpm, during regen the idle will bump up to between 800 and 900 rpm.
Complaints remain relatively low. We still love how the truck's Digital Steering Assist functions, however one of our staffers did manage to knock the steering slightly out of alignment (how on flat pavement we'll never know). Since we haven't yet been to the dealer to get it straightened, the wheel is now cocked slightly to the left, off-center, and canted. If GM's crooked steering wheels didn't bug you before, this one sure would. We'll get the alignment fixed shortly.
We're saddened by the prospect of this truck making its pilgrimage back to its rightful owners, but at the same time thrilled that there's still some time on the clock before this happens. We've got a couple big road trips planned and maybe a bit of hauling. Stay tuned!
Report: 3 OF 4
Previous Report(s): January/February, May/June 2019
Base Price: $59,600
Price as Tested: $73,730
Long-Term Numbers
Miles to date: 18,427
Miles since last report: 3,394
Average mpg (this report): 14.57
Test best tank (mpg): 21.09 (open highway, unloaded)
Test worst tank (mpg): 11.12 (towing 8,000 pounds up a steep grade)
Test Maintenance
Exhaust fluid refill at 6,000 miles.
Oil change at 7,792 miles.
Exhaust fluid refill at 14,000 miles.
Oil change, fuel filter, and DEF top-off at 15,050 miles.
Test Problem Areas
Logbook Quotes
"Sharp looking truck, love it!" - Random Parking Lot Guy
"What is it, about $65k?" - Another Random Parking Lot Guy
"Seriously, the spoofed spam phone calls to the truck's OnStar have got to stop."
"This truck is so much happier towing a load than it is hauling air."
"Hey look, the truck is in regen mode, again."