Engine hesitation/bog

[Balame]

Hi guys, 

My e28 m30b35 has an intermittent bog/hesitation at high revs around 4-5k rpm onwards. Mostly happens in first and second gear. 

Does not occur when the car is cold. Have changed the spark plugs, tested ICV, AFM & TPS and all seem to be doing their job.  

Any tips on what on what this issue could be?

Thanks in advanced!

[Shawn D.]

When was the last time you changed the fuel filter?  What's the running fuel pressure?  Does the AFM put out a smooth curve when moved through its range?