that's a little low in the rev range but "could" be what we call the Valley of Death   is the changeover point between Single small Primary and Parallel Twin turbo mode (both)   I'll see if I can find a Dyno graph of my BG5c in the garage thread or archives   photo bucket has eaten the images (but I know I have them @ work so please wait 10-12 hours hah  

perchance : a clue or a link  not easiest thing to search for eh ❤️   

It's always to get to a good baseline with service parts , I have had this issue before and the boost / map sensor switch solenoid wasn't switching in the black box I would check that for a start 

Any charts for the 2.5L engine with just a tune?