How They Made My 2021 Sierra AT4 Even More Bad A$$


There are many perks to working at a car dealership.

My favorite is the opportunity to drive the latest Sierra and Silverado’s 24/7.

I will drive one as a dealer demonstrator for 3-5 months unless it sells before then.

In 2019 the Sierra and Silverado got a major overhaul.

I’ve bounced between the Chevrolet Silverado High Country and GMC Sierra AT4 mostly.

Both trucks are on the higher end of the spectrum yet they are very different.

It was time to pick a new truck, we were low on inventory, so I chose our only 2021 GMC Sierra AT4 we had in stock at the time.  

Black wouldn’t be my first colour choice.  It looks unreal clean, but it never seems to stay that way.

My only MUST HAVE was the 6.2 V8 engine.

AT4.  6.2.  Let’s go!

When I was reviewing the options afterward I noticed a model code I wasn’t familiar with.  


Ryan Thompson General Manager and his AT4


The 6.2 V8 engine paired with the 10-speed transmission was always more than enough power to meet my needs.

But wait. What could this be?  I immediately reviewed the spec sheet and started to smile.

I hadn’t seen this option on any previous GMC Sierra AT4 spec sheets.

Off-Road Performance Package?

Included in the Off-Road Performance Package:

  • LT275/65R 18 Duractrac tires (we always order these on AT4 anyway)
  • (PDM) – Performance Upgrade Package
    • Performance Air Intake System
    • Cat-Back Performance Exhaust


Air Intake adds more power!

I am satisfied with the power and performance of the 6.2L V8 engine with Dynamic Fuel Management.

420 HP and 460 lb-ft of torque is more than enough most of the time.

But you don’t know what you don’t know, right?

By adding the cold air intake I gained an extra 15 horsepower and 9 lb-ft of torque. Transforming my daily driver into a 439 horsepower off-road powerhouse.

I noticed the difference immediately.

I had always loved the power and performance of the 6.2 in my previous demos, but this was VERY noticeable.


Performance Exhaust? Yes PLEASE!

The dual exhaust was nothing new as this is standard on the GMC Sierra AT4. But, adding the cat-back exhaust created the perfect rumble for my ears.

At first, I feared the exhaust may wake up the neighbors and be irritating to drive.

Not the case at all.

A nice sporty rumble puts a smile on my face each morning when I hit the remote start. It brings me back to the Borla Cat Back Exhaust we used to install on our previous-generation trucks.

Is it worth the extra $$?

For a little over $3,000, it’s a great value to get a factory installed cold air intake and super high-quality exhaust.

This won’t appeal to all AT4 buyers.

For most, the 6.2 with the 10-speed transmission is enough GET-UP and GO for their daily driver.

Already thinking of adding a cat-back exhaust?

Why not up the ante and get a few more horsepowers at the same time!


Considering a GMC Sierra AT4?  Don’t forget to check out its cousin, the 2021 Chevrolet LT Trailboss


Written by:


Ryan Thompson

General Manager

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