Question for you 5.3L guys

Let me put in some sound info. The LS platform was redesigned from the ground up on a fresh sheet of paper. The fuel efficiency comes from the new combustion chamber shape and intake port angles causing a swirl FAR beyond any sbc prior allowing compression ratios to go as far as 11:1 on regular 87 octane fuels if memory serves me correctly the escalade has 11:1 compression and makes over 400 hp STOCK. old sbc ended between 8.?? :1 and 9:1 ? I furget. Tuning a carb and distributer is a joke today. I see LS platforms in my shop regularly with over 300k that run like a top. Will you see 20 mpg in your old barn door in the wind? gl Id have to calc it myself to believe it.I don't get better that 18mpg overall avg with a DURAMAX in my 72 blazer and diesels are way more efficient. The reason a Corvette gets 28 to 30 is pretty friggin obvious to anyone with even a peanut for a brain (its very very aerodynamic) for those w said smaller brain onto other refinements. The ring pack has less tension (= less friction) The roller lifters = less friction, there are many other refinements adding to less friction and reciprocating weight (= mpg) the 5w30 oil = less friction. It goes on and on and on. The turn the key in any weather alone is the key seller for me.