I never could get good SG2 data from the Jeep, it's been stuffed in a box for the past year. The best I could tell, it's the fuel flow rate data point that's off. My SG2 would read 3-5MPG and <100Mi To Empty right at fillup time. It'd also report that the 3.6 had slurped 27gal from the 22gal tank. The miles traveled was spot on.
I went 'round and 'round with SG support, explaining
((TOTAL_GALS - (ACCURATE_MILES_TRAVELED / INACCURATE_AVG_MPG) = BAD_MTE))
They weren't interested in the issue.
As far as Decel Cutoff, I think the Jeep itself sends bad data, even to its own EVIC. Coming down off the mountain passes, I'll often shift into N and coast. The AvgMPG and MTE on the dash will both drop like a rock during the coast. Once back in gear, the values will rise to above where they were pre-coast. In other words, regardless of whether you can get any usable MPG data from the SG2, I don't think the Decel Cutoff bits will ever be read properly.