Try as I might, I honestly could not feel when the fuel management system switched the Hemi from 8 to 4 cyl. On the Ram, the driver info display includes only avg mpg, not current mpg, but you could still tell it was working because the avg mpg would start up noticably after a few mins on a flat stretch. I assume having the trans in 'Tow' mode keeps the engine on 8cyl and I was avg'ing 12.4mpg pulling the car hauler around the back roads. I saw a high avg of 19.5mpg after about 5min of slightly hilly 55-60mph unladen driving. My bigget complaint about this truck was the front edge of lower seat cushion was too high, rather uncomfortable for my short legs. Pretty good hike up into the cab as well.
Since posting I also discovered GM's 2007 5.3L is a multi-displacement engine, so I took one of them for a drive to compare. That engine management system was seamless going from 8 to 4 cyl. also. The neat thing about the GMC was their driver info display included instant mpg and a V8/V4 light. You could clearly see when it flipped to 4cyl and the effect it had on mpg. I was impressed to see the mpg up in the mid-30mpg's cruising along at 65mph. With a little practice, I could quickly lift off the accelerator pedal and 'kick it down' to 4 cyls, even if I had been cruising along previously and the engine management system didn't do it automatically for some reason.
I admit I was skeptical of the technology but walked away from both test drives impressed. Don't have the bank for a new diesel and this sure seems like it eases the gas V8 'pain at the pump' some if you need a truck. I would be very pleased to see 18-20mpg+ avg. That's 20% better than my old '05 Sierra 5.3L (R.I.P.). Might be kinda fun too if, after taking an earful from the treehugger next door about your big, new gas hog, that it gets gas mileage roughly on par with his wife's mini-van. /forums/images/graemlins/smile.gif