[redwngr]

Did they drive it with the computer connected?
If so, did the computer show that it was using high gears?

When you switch to M mode, can you detect that it is downshifting?

Usual GM programming includes a downshift when switched to M mode. If in 9 or 10 before the shift, it's not going to end up in M9 or M10 when switched to M mode. (the resulting gear will depend on current gear when switched, and if T/H is active at the time)

 

[redwngr]

If the took it up to 60 on the flat with the computer hooked up, it would seem likely that they checked what gear it got into.

Curious to hear more about this. Certainly sounds like it has an issue.

 

[redwngr]

There are write-ups for the 3 transmissions:

The Ford HD 10 speed 10R140, is not the same as the 10 speed in the 1500's and 150's.

Ford 10R140 TorqShift 10 Speed Automatic Transmsision Specs & Ratios


The GM HD 10 speed 10L1000,is not the same as the Ford 10R140 and not the same as the 10 speed in the 1500's and 150's.

GM/Allison 10L1000 10 Speed Automatic Transmission Specs & Ratios


The co-developed transmission used in the LD pickups is GM 10L80 and Ford 10R80

Ford 10R80 and GM 10L80 10 Speed Transmission Specs and Gear Ratios

Specifications and gear ratios for the 10R80/10L80 10 speed automatic transmission developed in a collaboration between Ford Motor Company and General Motors. The Ford 10R80 and GM Hydra-Matic 10L80 is currently used in a variety of fullsize vehicles by both manufacturers. The transmissions...

www.dieselhub.com

 

[redwngr]

Well guys. UPDATE. After 25 minute drive with Diesel tech and computer hooked up, no changes 13.2 mpg flat highway, tech was like that ain't right. Unhooked computer and left dealership. Drove 17 miles on relatively flat highway at 60 mpg, note 8 miles was the same we tested on. Bingo 27.2 mpg. And 19.6 mpg around town. Tech can't believe it. Same thing today. WTF.

Did the tech verify that it was not in regen when it was getting about 13mpg?