In the mid to late 70's, the EPA had chocked all the performance out of the American muscle cars, like I've posted before "The 1977 Dodge Aspen was faster than the '77 Vette, 400 TransAm, and Camaro"
To keep sales excitement in the depressed car market, muscle trucks were devised. Nowadays, very common with the Viper engined Dodge trucks, Cummings turbo-diesel trucks, 454 Chevy, Ford Lightning, etc.
The beginnings may well have been the Dodge trucks of '76, 77, 78, and '79. The Warlock, Lil Red Express, and something I've never heard of, the True Spirit.
360 cubic inch engines, 727 trans, and 3.55 gears. The engine was equipped with the W2 heads (high performance), Holley 4 barrel, Holley Aluminum Hi Rise intake... etc. Made 230 HP and 295 ft/lbs, did a 14.7 1/4 mile.
http://classicads.greatoldcars.com/classifieds.php?a=2&b=3993 for a Dodge True Spirit