I've posted before about this. I just had mine reflashed last month from AV to AX, so it's all pretty fresh in my head.
The EB in Tow/Haul mode with the AX flash feels about as strong as it did with the AV flash in regular mode. I live at the top of a small mountain, so I'm able to monitor my descent speed and EB efficiency on a daily basis.
The new flash is putting me at the bottom of the hill at 5-10 mph faster than the old flash using just the exhaust brake. Sucks, 'cause now I'm starting to coat/pit my new rims with brake dust. Didn't happen before.
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2007.5 Ram 2500 MegaCab 4x4, 6.7L, 68RFE, 3.73 gears, SLT, Line-X, Snugtop Extra Vision shell, Bilstein 5100s, 285/75-17 Toyos, Walker Evans wheels, Amsoil lube & bypass filter, PML rear diff cover & tranny pan, Dynatrac Free-Spin, Arab's kid's college fund