4.8 vs 5.3

[truck3]

My 2001 Silverado with the 4.8 gives me 18-20 mpg routinely. Mileage is higher when the driving has been mostly highway. I've been reading that the new (07 & 08) trucks with the 5.3 and cylinder deactivation (also called active fuel management) are supposed to get 20 mpg, a 20% improvement over previous 5.3 engined trucks.

Is there anyone in the group who can tell us what their "real world" mileage is with the 5.3 with cylinder deactivation?

Are there are any people in the group associated with GM who can address the engineering or marketing decisions of the company? Why doesn't GM offer cylinder deactivation on the 4.8 as well as the 5.3. A 20% increase could make 24 mpg possible. Wouldn't a full size pickup with a 24 mpg rating be a huge selling point?

[4gstarion]

i drove a new tahoe and suburban 08 model both for 3 weeks and they get about 20mpg the cylinder shuting 4 kinda helps but i dont c a big difference