Image: WIkipedia

I have a few ideas, but does anybody know for sure?

GMT400 of course refers to the ’88-’98(ish) body style pickups and related SUVs, and it’s a much better term than that “OBS” crap. Wikipedia and other sources mention a GMT480 that is “similar”. How so? What’s the difference?

Wikipedia’s GMT400 page shows that there are several submodels that fall under the GMT400 series. For example, the Chevy Suburban is GMT410, but the GMC Suburban is GMT425. Could GMT400 be Chevy only, and GMT480 indicate the GMC version?

The ordering of the GMT4XX numbers is kinda throwing me off here. There’s a 410, a 415, and a 420 (all Chevys). Then there’s a 425 and a 430 (both GMCs). Then a 435 for Cadillac. I wouldn’t expect GMC pickups to have a number so far away from the rest. It’s as if 480 was meant to be something very separate from the standard offerings.

Could it be for the medium-duty Kodiak/Topkick commercial trucks? No, those would be GMT530s. How about 3500HDs? Google tells me that those are actually GMT455s, a number absent from Wikipedia’s list.

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Sure, there’s always a chance that Wikipedia was erroneously edited at some point. It’s apparently missing some information, and no sources are listed for any of these numbers. Maybe we need a more authoritative source...

Wait a minute, what about 4WD vs 2WD? Could 480 be there to differentiate 4WD from 2WD models, like the “K” and “C” designations do? Doubtful- there appears to be no such separation among Suburbans (unless there are even more GMT4XX numbers missing from the list).

And there are too many different cab/bed configurations for 480 to simply be a LWB version of the 400. So what does it mean?

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EDIT: It might be worth mentioning that the GMT800 generation of trucks uses an “880” designation for HD models. However, the Suburban’s “830” designation doesn’t line up with the GMT400 generation.

The biggest clue that I’ve managed to dig up so far is an Automotive News article from 2000 that mentions the GMT480 as having been built alongside 450s (?) and 455s: [possible paywall alert]

The Flint, Mich., plant also is receiving a major overhaul on the Chevrolet C/K and Sierra. The trucks are changing platform from the GMT-450, GMT-455 and GMT-480 platform to GMT-800. When the plant returns to production Aug. 28 it will make the Chevrolet Silverado, the updated version of the C/K, and GMC Sierra.

If this information is accurate, it could be a big step towards solving this mystery...