I think nobody here locally have those kind of knowledge. Did you just do a block swap? No other things changed?
Why didnt you swap with a similar M54B30 as there are many around? I saw a for sale ad yesterday, M54B30 with gb and wiring for 6500. There are many B30 available. I understand its water under the bridge, swap already done, just wanna understand it.
Maybe you can meet up with somebody on here with a M54B25 to compare responsiveness.
Anyway, message me at 019-2652830 so i can add you to our e39 whatsapp group.