I take my chances with 0W40 all day over 0W20.
I have seen the loading on the 6.2l at highway cruise and it is not pretty.
0W40 oil pressure at idle 35 PSI, cruising 45 PSI not significantly different than 0W20, but the 0W40 has far better film strength, tolerance to fuel dilution and better HTHS protection. 5w30 does not offer a tremendous jump in the HTHS protection, it is closer to 0W20 than 0W40.
Not going to suffer an oil related failure from 0W40 as long it is changed frequently.
Interesting the GM TechLink info on capacities and oil requirement.
The Camero and Corvette 6.2l list 0W40, I guess if it good enough for these engines it should be good enough for the L87 in the trucks.
Also note how many models are speced for 5W30.
GM TechLink Oil Info