With the third generation Rounded-Line C/R & K/V models, the Suburban became a four-door vehicle. The Rounded-Line 1970s body style remained largely unchanged for 19 model years – making this series the longest Suburban generation in production. 2WD (C/R) and 4WD models (K/V) were both available in 1/2 and 3/4 ton ("10" and "20") chassis.

Suburbans for model year 1973 now had two doors on each side (the previous generation had just one door on the driver's side), front-and-rear air conditioning, a baggage rack, a heater under the third seat and step-plates for easier access. A new Eaton Automatic Differential Lock was introduced as an option extra for the rear differential.

For the 1973 model year, the base engine was the 250 CID inline-six (100 net HP), with a 307 or 350-cubic-inch small-block V8 (115 or 155 net), or the new-for-1973 454 CID big-block V8 (240 net HP) optional. The 307 V8 was dropped for 1974, supplanted by the 305 and 400 small block V8's in 1976. The 400 was dropped after 1980, leaving the 350 as the only available engine in K-series Suburbans as the 454 was not yet offered in 4x4's. In 1982 a new 6.2 L (379 cu in) Detroit Diesel V8 engine was available, producing 130 horsepower and 240 lb.-ft. of torque. The Diesel later became the engine of choice for Suburbans exported to Europe from USA. Except for the discontinuation of the 305 V8 in 1988, the engine line-up continued mostly unchanged, with the 350, 454, and 6.2 diesel, until the Suburban was redesigned onto the GMT400 chassis in 1992.

Three-speed Turbo Hydra-Matic 350 and 400 automatic transmissions were available, and the four-speed Turbo Hydra-Matic 700R4 was introduced in 1981 and was available with the small block and 6.2-liter diesel. Towing packages, with lower axle ratio and heavy-duty cooling additions, were optional.

Trim options included the base model ("Custom Deluxe" before 1975, "Scottsdale" or "High Sierra" after) and the upgraded ("Cheyenne Super" before 1975, "Silverado" or "Sierra Classic" after) versions. Optional 2nd and 3rd-row bench seats allowed for nine-passenger configurations.

A popular "endgate" option was offered to replace the conventional swinging panel doors. The endgate included a hidden manual crank handle on the exterior for lowering the rear glass. Endgates could be ordered with an electrically-operated window regulator to replace the exterior crank, which used a key to operate. Once the rear glass was down, the endgate became a pickup-style tailgate that folded down for cargo loading.

Rear floor heat and ceiling air conditioning systems were optional. The standard 25-gallon fuel tank could be replaced with 30 gallon (from 1973) or a 40-gallon (from 1974).

For model year 1981, automatic locking front hubs were added for shift-on-the-move four-wheel drive models, and the NP208 transfer case replaced the NP205 in most models.

For 1984, asbestos was removed from rear brakes. For 1985, a new grille was used. A total of 64,670 Suburbans were made in 1985.

For model year 1987, the method of fuel delivery for the engines was switched from carburetors to electronic fuel injection. (However, for the 454 cubic inch or 7.4-liter displacement engine, carburetors were still made available along with electronic fuel injection for the 1987–1989 model years). The system that GM chose was called throttle body injection, or TBI. Suburban gained rear-wheel anti-lock braking system (ABS) for the 1990 model year. A heavy-duty four-speed automatic transmission, the 4L80-E was added for 1991. Also for 1989, the grille was redesigned to accommodate a quad side-by-side headlight setup and larger marker lights/turn signals than the previous dual filament single headlight setup, which was styled concurrently with the GMT400 light duty trucks. Economy models (usually for fleet usage) were available with only two headlights (again, based on the base model C/K series).

GM temporarily changed the usual "C/K" designation to "R" and "V" for the 1987 through 1991 model years. This was done to avoid confusion with the GMT400-based Chevrolet C/K pickup trucks, which were introduced in 1987, during the overlap period.