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  • Long-Term Report 1: 2018 GMC Sierra 2500HD Denali

Long-Term Report 1: 2018 GMC Sierra 2500HD Denali

Long Term Report 1 of 4

Sep 17, 2018
Photographers: Jason Gonderman
It’s always exciting to welcome a new vehicle into our long-term test fleet, especially when it’s the winner of our 2018 Pickup Truck of the Year test. The truck we’ll be testing for the next 12 months is an ’18 GMC Sierra 2500HD Denali equipped with the new L5P Duamax diesel engine. When we placed the order, we checked all of the same boxes as the one on our test, the only exception being paint color. Naturally, we picked the most expensive color option, White Frost Tricoat, which adds $995 to the sticker but looks amazing.
We began our time with the Sierra with the epic 3,000-mile road trip that we featured in the previous issue (November/December 2018), and this report picks up from there. During our cross-country drive, we saw fuel-economy numbers tip into the low 20s, which is quite impressive for a nearly 8,000-pound truck with the aerodynamics of a barn. Back in the city, things have settled into a groove with the Sierra averaging between 12 and 14 mpg in combined city and highway traffic driving.
Photo 2/20   |   What was initially thought to be a 12,000-pound load turned out to be more than 17,000 pounds. Oops. Thankfully, the Sierra was up to the task and hauled the load 5 miles to the scrap yard without complaint.
Tied with fuel economy for most asked-about topics is that of exhaust regeneration. Diesel pickup emissions technology has come a long way since the introduction of the first diesel particulate filter in 2007. The L5P Duramax utilizes the same “9th Injector” method for filter regeneration as the previous LML did. Simply put, the truck uses a fuel injector mounted in the exhaust stream to feed raw fuel to the particulate filter during regen cycles to aid in burning off accumulated particulate. During our time thus far with the Sierra, we’ve only determined two ways tell if the truck is in active regen, and both are during street driving. First, the engine rpm will raise from a normal idle of about 650 to around 850 rpm. While this may not seem like much, it’s enough to cause erratic shifting while coming to a stop, say at a red light. And second, if the truck is shut down mid-cycle, a very noticeable burning smell can be detected near the passenger rear door, which is where the DPF is located. Other than those two scenarios, DPF regeneration is undetectable to the senses and doesn’t produce the sharp drop in fuel economy seen in previous generations. We’ll talk exhaust fluid in our next report.
Photo 3/20   |   We’ve been fans of GMC’s backup camera and 8-inch screen for a number of years. The resolution is fantastic and helps greatly when hitching a trailer.
Photo 4/20   |   All work and no play—well, you know. GMC’s White Frost Tricoat looks amazing among the pine trees, and Sierra’s locking rear differential makes getting to them easy.
Not wanting to baby an HD truck, we immediately put it to work. When a family member asked if we could help haul a flatbed trailer loaded with what we thought to be 9,000 pounds of scrap metal, we jumped at the chance. Our Sierra has a maximum conventional tow rating of 13,000 pounds (14,800 pounds with a fifth wheel), so an estimated 12,000 pounds of total weight should have been a workout for the truck. During our short 5-mile drive on flat ground, the truck barely broke a sweat. The integrated exhaust brake works wonderfully, and shifts were firm and confident with Tow/Haul engaged. As it turns out, once we crossed the scales, the load was north of 17,000 pounds—oops! While we can’t recommend knowingly overloading a truck, our Sierra handled it like a champ.
After the scrap trailer, we hitched up a relatively light 7,000-pound Airstream trailer. During a 700-mile drive on mostly open highway and mountain roads, we actually averaged better than normal fuel economy, go figure.
The first quarter with our Sierra 2500HD Denali has been delightful. The truck is quiet, comfortable, and extremely capable. Fuel range is solid, averaging more than 400 miles per tank, and economy is nothing to complain about. We look forward to the rest of our time together, as thus far it has proved itself deserving of the Pickup Truck of the Year title.
Photo 5/20   |   We’ll address the issue of exhaust fluid, and what happens when the tank runs dry, in the next report.
Photo 6/20   |   2018 GMC Sierra 2500HD Denali Exhaust Fluid Gauge

Report: 1 OF 4

Previous Report(s): N/A
Base Price: $55,850
Price as Tested: $57,995
Long-Term Numbers
Miles to date: 7,399
Miles since last report: 4,325
Average mpg (this report): 13.22
Test best tank (mpg): 18.97 (open highway, unloaded)
Test worst tank (mpg): 11.12 (towing 8,000 pounds up a long winding grade)
Test Maintenance
Exhaust fluid refill at 6,000 miles
Test Problem Areas
None
Logbook Quotes
“Truck smells like burning garbage again, must have stopped mid-regen.”
“Yay for Costco not stopping the diesel pump. Boo for a tank costing north of $130.”
“Another incoming spoof call to OnStar? Really?”
“I remember again just how much I love the 4GLTE service. Having fast Wi-Fi everywhere I go is amazing.”

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