Whether Chevrolet or GMC, the General’s third-generation, “square-body” trucks were a dramatic departure from the company’s previous efforts. The third-gen models featured squared-off front and rear fascias, subtle body contours honed by wind-tunnel testing, a more accommodating and ergonomic interior, and even an available crew-cab body, a style decades ahead of its time.
With that in mind, what follows is a quick, high-level overview of the third-generation C/K truck—be it two-wheel-drive C10/C20/C30, or four-wheel-drive K10/K20. We’ll take a look at model differences year by year but also highlight special editions, so you’ll know which examples are best for you!
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I bought a brand new 1973 K20 350 4-sp. It got 9mpg. I had to get out and lock the hubs in the icy wind, snow and slush, as I lived in Alaska. That's the way it was back then. It was one stiff rig. These trucks also rusted out in a big hurry.
These are the best designed trucks for a truck used for working. Very Solid with enough power to do the job. I have owned several of these trucks: 73, 76, 77, 79, 84, 88, 89. The 73 I had to replace all the sheet metal including the entire cab, other than that I had no other rust issues. Any of these trucks will out work anything you can buy today. I currently am using a 2014 ford and the body is very flimsy, doesn't take much to dent it. I guess if you want a vehicle with car options, the newer trucks are okay; but, I want a vehicle to get the job done for a reasonable price. I still drive a 73 GMC K25 350, 76 GMC C35 350, 79 C15 250, 88 V35 454, 89 Chevy R35 350. I also drive a non-square 06 GMC and it doesn't compare for durability. Especially the plastic clutch pedal/master cylinder assembly.
Internally during development at GM, these were known as “round body”. The “square body” moniker is of recent use.
I drove a new ‘73 and the first time it rained, water poured in at the top of the doors... no rain sill. What were they thinking? A subsequent add-on sill was added. As stated, this truck ended Chevrolet’s reputation and the rise of Ford. I owned a very low mile ‘86 C20, and the fit and finish and build quality were dismal.
Crew cabs soldiered on until ‘91 with this body, btw.
Unfortunately for gm this was the beginning to the end for gm’s trucks as they were rust buckets and that diesel was an awful attempt at a diesel. As a gm owner of cars and trucks forever I changed to Ford pickups which lasted from 1978-2007 when I finally came back to Chevy which I still drive today my 2008 Silverado has 187,000 miles on it. It has sat outside for 12 years and not an ounce of rust anywhere, and runs great with minimal maintenance. Those square bodied trucks from GM cost them a lot of $