Hi, I'm newish to performing ecu tuning but have been studying the theory basics for a while and have some basic knowledge.

I've been trying to get to the bottom of why my stock VAG 3.0L DDXC engine with auto 8 speed ZF uses approx 10% more fuel in 8th gear than in 7th gear, so I've been logging data for a while trying to get to the bottom of it. The vehicle is low kms (8000km) and no modifications have been made to the vehicle (other than an LED light bar). The vehicle recently did a 2000km journey across what is mostly very flat terrain and did a couple of full regens during this trip, but problem remained. The below image shows what I've found, that at highway cruise speeds in 7th there is no post injection (0mg/str) but in 8th this comes on at approx 3.0mg/str. Whilst I strongly believe this is causing the increase in fuel consumption, I don't know what is triggering it other than maybe a passive DPF regen setting.

Has anyone experienced this phenomenon and been able to rectify the issue with a tune setting? Can anyone confirm my theory and help with what tuning function can best help? I'm not really a fan of DPF delete but would like to turn off passive mode if this is an option?