Tire pressure Question??

[k2c1959]

i am going to throw this out over here since this is where the majority of my time and most people on these boards seem to hang. Gimme some feedback here if anyone has any ideas on this....
this may sound like a stupid question but hey, here goes anyway.
i have a 2004 GMC sierra z71 ext cab 1/2 ton,(My daily driver) recommended tire pressure says 45 psi in door tag. Today i bought a new set of pro comp at's and was watching the guys putting them on and they were inflating the tires to 80 psi!! that is the pressure recommendation on the tires (10 plys) E load rating. I argued the point with them about running 80 lbs in the tires and they said it was recommended and should be run at that!! am i just crazy here or should they be run at 80 lbs. truck feels like it is on roller skates...I'm thinking 80 may be great if towing or hauling a load, but that is overkill for highway driving. am i wrong here, does anyone know? im thinking they need to be dropped down to 45 as GM recommended, they are the stock size that came on truck, just a different brand. Let me have it.