Can't say I've noticed anything like you mention. Although I've only had my E90 for a couple months. I've just recently dialed it in with the correct JB4 map and E85 ratio. I usually flog it through a few gears at least once a day and it seems to be fairly consistent... FAST!
2008 E90 TiAg w/ Sport Package
JB4 G5 ISO/BMS OCC/BMS DCI/RL DPs/CP-E CP/Tial BoV/VRSF 7" FMIC/Walbro GSL392/423rwhp & 432tq