It stays unlocked for a short time. For example on mine it's unlocked until 1300rpm, then it's fully locked. In stock form it is unlocked until 1100rpm, then there's partial lock and it is fully locked only at 3400rpm.
So, yes, it lowers an ATF temp.

 

JLR transmission calibration is VERY "conservative" comparing to other 6hp like bmtroubleyou or vw.

 

Yes. Or you can buy the equipment yourself, but it's rather expensive.

 

I've finally managed to get this done on my 6HP26 4.2 XKR. I've got sticky Michelin Cup 2 305 tyres, Quaife LSD, fully bespoke suspension and over 600 pounds lighter than stock, so there's no traction issues here. No data to provide yet, but immediate before and after comparison with 9 miles done on the TCM tune and I can tell there's a massive difference. First the up shifts are much faster and torque feels significantly increased as if a restraint's been removed. It certainly doesn't feel like the same car. The car doesn't hesitate getting up to ludicrous speeds in seconds and feels like there's still gobs more torque available. I'll spend some more time with over the long weekend and perhaps try some Dragy data.

 

Has anyone done the reprograming on the 6HP28?