Stock Top Speed?

[Nashoba]

Applied a 93 octane tune for my 2005 5.3L Avalanche; bought a NOS system and had a 75 horse shot installed; dyno'ed at 336 hp at the rear wheels and ran strong up to 153 mph and still pulling when they shut it down. Never ran it past 130 on the speedo. Was commuting long distance a lot back then and was tired of those lifted F250 diesels running away from me when I maxed out at 100. Also put tires rated at 150 mph or so on the truck to keep from having a blowout. Was lots of fun. Expensive, though, as it cost $125 or more every tank of fuel and it took a whole tank to make the trip back and forth to work every week for the 479 mile commute.

 

[swathdiver]

My '79 Sportcoupe would get squirrely at 125 mph and the GNs would feel the same at 148 mph @ 4400 rpms. My '06 SV6 Sport Montana would get 21 mpg at 90 mph and I think it topped out/cut off at 100. My '93 Olds Ciera cut off at 104 mph. I've had the Yukon up into the 90s to pass but didn't want to flog it until I grease the driveshaft and check the u-joints. That guy having his driveshafts come apart on another forum curbed my enthusiasm too. If it improved our mileage I might be persuaded! LOL That Montana would get better gas mileage at 77+ than at 70.

 

[Nashoba]

Most vehicles have a "sweet spot" for best mileage and it is hardly ever at 65 mph, more likely at 70 to 75 mph.

 

[HiHoeSilver]

Most vehicles have a "sweet spot" for best mileage and it is hardly ever at 65 mph, more likely at 70 to 75 mph.

Yeah, we've had this discussion a few times and I think the general consensus is the 67-71 range. Obviously, your gearing matters, too.