General Motors completely revamped its Suburbans for 1973. Simple, bold lines accented with a distinctive bodyside molding marked the exterior of the new trucks, which now had four doors. The redesigned interior featured a dash angled slightly toward the driver. A full-time four-wheel-drive system was available and ideal for those who lived in areas of the country prone to slippery driving conditions. Trim levels remained the same as before and engine choices ranged from a 100-horsepower 250 c.i. inline six to a 240-horse, 454 V8. Keep in mind that after 1971, horsepower figures were given as net (installed engine with accessories) versus gross (just the bare engine) figures.
   1975 models were distinguished by a grille with larger internal rectangles along with a restyled tailgate. Trim levels were changed and now comprised base Custom Deluxe (why a base version was called "Deluxe" is a mystery), Scottsdale (with cloth seats and chrome exterior trim) and Silverado (with woodgrain interior accents, carpeting and additional exterior accents including wheel lip moldings). Corresponding GMC trim levels were, in ascending order, Sierra, Sierra Grande and Sierra Classic. Catalytic converters debuted (on non-heavy-duty trucks) to meet more stringent emissions standards, as did a high-energy ignition system and an optional (for four-wheel-drive models) 400 c.i. V8 with 175 horsepower.
   1977 brought a revised grille insert, where the former 32 small rectangles gave way to 15 larger ones. A new 305 c.i. V8 rated at 145 horsepower was available behind that grille.
   1978 marked the introduction of the 350 c.i. V8 diesel that became optional on the half-ton (C10) two-wheel-drive model. Minor changes to the interior, such as new seat fabrics and dashboard trim, also took place this year.
   Not much happened in 1979 except that the parking lights were now incorporated into the front grille/headlight facade.
   A more noticeable grille restyle took place for 1980 that featured square openings (instead of the previous rectangular slots) and, on Silverado models, square headlamps. A thermostatic cooling fan increased efficiency by running only when needed.
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   A nose job and a weight loss program improved the 1981 Suburbans. New, more aerodynamic sheetmetal from the windshield forward was grafted onto the truck, and the new fenders flanked a restyled grille with square headlamps (now on all models). Lighter materials helped reduce weight by as much as 300 pounds, depending on the model. A revised interior featured a new instrument panel, seats and door trim. A new 305 c.i. V8 with Electronic Spark Control debuted. The spark control allowed higher compression and power output (160 horsepower) that was equal to or better than the available 350 V8's numbers, with the advantage of better fuel economy. The 400 c.i. V8 was dropped, but still offered were the inline sixes (250 and 292 c.i.), a couple of 350 c.i. V8s and the stout 454 c.i. V8.
   A new 6.2-liter (GM started using metric engine sizes at this point) diesel engine debuted in 1982. A much stronger and reliable engine than the old 5.7-liter (350 c.i.) version, the 6.2 was offered with both two- and four-wheel-drive as opposed to the 5.7, which was only available on two-wheel-drive Suburbans. A four-speed automatic gearbox was a new option that promoted less engine wear and better highway fuel economy.
   Only sharp-eyed enthusiasts would be able to tell what changed for 1983: parking lights were relocated from the bumper to the bottom edge of the grille, which was now blacked out. Additional rust protection was provided by the use of anti-corrosion steel under the hood and at the front of the pickup box.
   1984 saw more steps taken (such as galvanized inner door panels) to fend off rust.
   A revised grille design with a thicker horizontal divider marked the 1985 trucks.
   The only changes for 1986 were redesigned engine seals on all "V" type engines, except the 7.4-liter (454 c.i. in old-fashioned terms) V8.
   1987, the last year of this long-lived (15 year) generation, saw the debut of throttle-body fuel injection (TBI) for all gas engines. As a result, the 5.0-liter (305 c.i.) and 5.7-liter (350 c.i.) V8s were more powerful, kicking out 170 and 210 horsepower, respectively. After decades of using the C and K nomenclature to indicate two- or four-wheel drive (for example, C10 Suburban), Chevy and GMC changed the two-wheel-drive truck's "C" to an "R" and the four-wheel-drive truck's "K" to a "V."
   Although GM completely redesigned its full-size pickups for 1988, the Suburbans, which up to now were basically station wagon versions of the pickups, were unchanged and would have to wait four more years for their overdue overhaul.
   A host of under-the-skin improvements took place in 1990. The 7.4-liter V8 was fitted with electronic spark control, and the 5.7-liter V8 received upgraded piston rings and intake valves. Antilock rear brakes debuted this year. In an effort to simplify ordering and production processes, many formerly individual options were now either added as standard equipment or grouped together in packages. The Cheyenne model had tinted glass, halogen headlights, a larger (34 gallon) gas tank, AM radio, intermittent wipers and instrument panel gauges added to its standard equipment list. Scottsdale got rally wheels, a custom steering wheel and bright grille trim. And Silverado had its standards raised with the inclusion of floor mats, a sport steering wheel and an AM/FM stereo radio. Corresponding GMC models received the same upgrades.
   The 7.4-liter V8 was refined for 1991 with tighter combustion chamber tolerances and improved oil pan gaskets. A new automatic transmission was introduced for heavy-duty trucks. This four-speed automatic gearbox, dubbed "4L80-E," featured electronic control and the ability to handle 440 foot-pounds of torque.
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