I know that the fenders are different, and the 99-02 Chevy hood will fit the GMC front end if you trim it for the headlights. I've seen a Chevy HD hood on a GMC before and it looked tight.

 

man those hd hoods are killer, they are so awesome, i just cant find one anywhere

 

the chevy hoods dip down pretty steep in the front compared to the sierras and it makes it hard to cut a stock chevy hood and make it fit takes alot of patience and skill that i lack lol

af far swapping from chevy to gmc when i did my 99 i needed, fenders, hood, grille, bumper, bumper trim, bumper valance, foglights are different(that was unexpected), headlights and turn signal lights

everythign else will fit right up to eachother same number of bolts and everything

if your interested i have a goodhoods ram air hood i've been toying with selling and getting a reg cowl. or stock sierra hood (i'm going for the sleeper stealth look) send me a pm if you want a pic of it