I don't think this applies to the SHO 3.5l, they make multiple 3.5l displacement engines and I know the 2018 5.0l truck has the dual injector set up. I'm sure I had read that they stated another reason for the extra set of port injectors but even if it's an after effect it's a good thing. I had an intake plenum off a 2017 5.3l Tahoe a few days ago for bank 1 injector replacement (different flow rate between banks issue) and with only 33k miles the valves have heavy deposites on them. I think it's just the nature of direct injected engines combined with a lot of blow by gasses (and our turbo's don't help the later). Short of methanol injection to help wash things down, catch cans, quality oil and fuel seem to be the only band aides.
Edit-"Duel Fuel Deliver System combines Port Fuel and Direct Injection fuel in the combustion chamber for improved efficiency, performance and reduced emissions". Nothing about washing down the valves, but if you've seen what I've seen, you know it's a factor. The big question to me is, other than a chunk of that shit breaking off and getting sucked through the engine and turbos, how much of a factor is it? In the past, the issue with coking the valves on port injected engines dealt with fuel saturation on the contaminated back side of the valves, but on D.I. engines the only thing flowing over the valves is air and the offending blow by gasses.
