Pretty sure the engine cover on the 2005 Sierra Denali trucks is just the normal Vortec cover, then in 2006 and 2007 classic it had the Vortec Max engine cover. I have looked at 4 or 5 2005 Sierra Denali pickups and none had Vortec Max cover.

And FYI, the 2wd Vortec Max trucks could have 4.10's as well.

2wd Vortec max? - SilveradoSS.com - Page 2

 

The Red Vortec Max cover started in 2006 when they changed the name from Vortec High Output to Vortec Max.

The early ones just said Vortec 6000 in silver

Starting in 06 The V-Max had optional gear ratios and you could get the package in 2wd and 4wd. You could also now get that package in a crew cab as well.

The prior 04-05 Vortec High Output were only availible in 2wd extended cabs and 3:73 was the only ratio for that package.

 

It sort of depended on the year model and whether it was the truck or SUV. The 2001 Sierra C³ had 3.73’s, as did all year models of the GMT-800 SUV versions. The Sierra Denali’s starting with the 2002 Quadrasteer models were all equipped with a 4.10 axle ratio and this was carried on through the end of the GMT-800 series SD’s.

 

Well, Just the trucks and not the Quadrasteer option.

Sorry I am not as versed on the GMC C3 and the Denali