Based on data from 77 vehicles, 5,444 fuel-ups and 1,760,465 miles of driving, the 2021 GMC Sierra 2500 HD gets a combined Avg MPG of 13.18 with a 0.10 MPG margin of error.

Any Engine Type 6.6L V8 DIESEL (59) 6.6L V8 GAS (17) Any Body Style Extended Cab Pickup (1) Crew Cab Pickup (16) Any Submodel Base (3) SLE (7) SLT (10) AT4 (26) Denali (31)

Below you can see a distribution of the fuel-ups with 26 outliers (0.48%) removed.

Following shows the average MPG of each of the 77 vehicles in the system.

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• My Sierra 2500 HD

  2021 GMC Sierra 2500 HD Denali 6.6L V8 DIESEL Automatic 10 Speed
  Added Jul 2024 • 50 Fuel-ups

  Property of josterhout1

• 15.9 Avg MPG

• My Sierra 2500 HD

  2021 GMC Sierra 2500 HD SLT 6.6L V8 GAS Automatic 6 Speed
  Added Jan 2021 • 287 Fuel-ups

  Property of kbeazley

• 10.6 Avg MPG

• My Sierra 2500 HD

  2021 GMC Sierra 2500 HD SLE 6.6L V8 GAS Automatic 6 Speed
  Added Nov 2024 • 61 Fuel-ups

  Property of Anticyclone

• 11.7 Avg MPG

• 2021 - GMC AT4

  2021 GMC Sierra 2500 HD AT4 6.6L V8 DIESEL Automatic 10 Speed Crew Cab Pickup
  Added Sep 2024 • 16 Fuel-ups

  Property of Landmans

• 15.0 Avg MPG

• AT4

  2021 GMC Sierra 2500 HD AT4 6.6L V8 DIESEL Automatic 10 Speed
  Added Jul 2025 • 16 Fuel-ups

  Property of ericmkolar

• 14.4 Avg MPG

• My Sierra 2500 HD

  2021 GMC Sierra 2500 HD Denali 6.6L V8 DIESEL Automatic 6 Speed
  Added Jan 2025 • 27 Fuel-ups

  Property of keenwyatt

• 14.4 Avg MPG

• My Sierra 2500 HD

  2021 GMC Sierra 2500 HD Denali 6.6L V8 DIESEL Automatic 10 Speed
  Added Sep 2025 • 43 Fuel-ups

  Property of mdr004

• 15.4 Avg MPG

• My Sierra 2500 HD

  2021 GMC Sierra 2500 HD Denali 6.6L V8 DIESEL Automatic 10 Speed
  Added Apr 2023 • 162 Fuel-ups

  Property of bcfiremedic

• 12.1 Avg MPG

• BigTruck

  2021 GMC Sierra 2500 HD 6.6L V8 GAS Automatic 6 Speed Crew Cab Pickup
  Added Mar 2023 • 84 Fuel-ups

  Property of pmhanson

• 13.4 Avg MPG

• 2021 Sierra 2500HD

  2021 GMC Sierra 2500 HD Denali 6.6L V8 DIESEL Automatic 10 Speed Crew Cab Pickup
  Added Jan 2024 • 102 Fuel-ups

  Property of Bost05

• 12.6 Avg MPG

• 2500Hd GMC

  2021 GMC Sierra 2500 HD AT4 6.6L V8 DIESEL Automatic 10 Speed Crew Cab Pickup
  Added May 2021 • 171 Fuel-ups

  Property of jmgolden1978

• 14.1 Avg MPG

• Truck

  2021 GMC Sierra 2500 HD AT4 6.6L V8 DIESEL Automatic 10 Speed
  Added Nov 2024 • 44 Fuel-ups

  Property of MontanaRaptor

• 13.8 Avg MPG

• Sierra 2500 HD

  2021 GMC Sierra 2500 HD Denali 6.6L V8 DIESEL Automatic 10 Speed
  Added Apr 2025 • 11 Fuel-ups

  Property of Dcline8192

• 11.9 Avg MPG

• DENALI 2021

  2021 GMC Sierra 2500 HD Denali 6.6L V8 DIESEL Automatic 10 Speed Crew Cab Pickup
  Added Dec 2020 • 145 Fuel-ups

  Property of rivcoinc

• 14.2 Avg MPG

• GMC

  2021 GMC Sierra 2500 HD Denali 6.6L V8 DIESEL Automatic 10 Speed
  Added Jul 2024 • 34 Fuel-ups

  Property of JK27

• 12.9 Avg MPG

• GMC Sierra 2500 AT4

  2021 GMC Sierra 2500 HD AT4 6.6L V8 GAS Automatic 6 Speed
  Added Mar 2022 • 108 Fuel-ups

  Property of 22GMCAT4HD

• 12.2 Avg MPG

• 21 Denali HD

  2021 GMC Sierra 2500 HD Denali 6.6L V8 GAS Automatic 6 Speed
  Added Apr 2021 • 58 Fuel-ups

  Property of shreff86

• 11.2 Avg MPG

• My Sierra 2500 HD

  2021 GMC Sierra 2500 HD 6.6L V8 DIESEL Automatic 10 Speed
  Added Apr 2025 • 80 Fuel-ups

  Property of subie-doo

• 13.7 Avg MPG

• AT4 Whore

  2021 GMC Sierra 2500 HD AT4 6.6L V8 DIESEL Automatic 10 Speed
  Added Mar 2021 • 193 Fuel-ups

  Property of pigpen23

• 12.6 Avg MPG

• Big Bubba. My Sierra 2500 HD

  2021 GMC Sierra 2500 HD AT4 6.6L V8 DIESEL Automatic 10 Speed
  Added Jun 2021 • 124 Fuel-ups

  Property of moose57

• 16.3 Avg MPG

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