I really thought the 2.7 would be the better engine for this configuration than the 3.5. It’s not like the 2.7 is lacking in power, and IMO the stiffed iron/carbon block would be the stronger material. Otoh, the 3.5 would make sense if it can go into Adkins (?) cycle.
@ctechbob - everything you said above is same answer as the Toyota system, except maybe the water pump. I need to look that up. It might be the same too. 8 speed trans with a motor/gen in place of the TC, and it uses multiplate clutches to handle engagement.
Your MPG is incredible. I hover at 23.8-23.9, in a smaller truck, 5300 lbs curb weight.