As often happens, the GMC Envoy's name first debuted as the top trim level on another vehicle -- in this case, the GMC Jimmy, itself sharing a chassis with the Chevy Blazer. By 2002, the Blazer had been replaced by the Trailblazer, and the Envoy replaced the Jimmy. Since then, the Envoy has been filling a special fat niche in the market, competing directly against the Ford Explorer while offering GM power and sophistication.
The GMC Envoy of this generation used a mixed suspension, with coil-over struts up front and more traditional, separate coils and shock absorbers in the rear. There's good reason for the difference in suspension types; in the rear, GMC offered both standard coil springs and load-leveling air springs that kept the SUV's hind quarters up while fully loaded or towing.
The factory front strut is AC Delco part number 903015RS; Rock Auto lists them for $131.79 as of early 2014, which is about $20 more than the best-selling Monroe strut -- part number 171341 -- and more than double the price of the cheapest FCS 1336324. The most expensive front strut is the heavy duty, $202 Gabriel G57022 from Autozone. As you might expect, the Monroe and struts in its price range and higher offer better handling and a better ride, and are far preferable for Envoys without the rear air suspension. If you're just looking for a boost in handling, you can upgrade the shock absorber inside the strut with an AC Delco Sport unit; the specific part number varies by the vehicle and options.
In back, The stock replacement shock absorber is AC Delco part number 520409, which Rock auto lists for $40 a piece. More expensive sport units from AC Delco and other manufacturers like Monroe and Gabriel run upward of $75 a piece, and the aftermarket Rancho RS5000 off-road shocks offer good performance value for about $47 a piece. Rear coil springs, Westar part number CK-7626 run about $325 a pair from Autozone, and the air spring bags -- Westar part number AS-7056 -- cost about $215 a pair.
