altec,
Highway cruising speed for me is usually 80-100 kph, which translates to only 2,000 rpm. However, I occasionally reach 3,000 rpm when overtaking slow vehicles in 2nd or 3rd gear. Also, I haven't used biodiesel for over a year owing to the lack of suppliers in Pangasinan. So far, I haven't noticed any degredation in engine performance, and smoke belching is still rare for me even without BD.
I sometimes reach 130 kph on the NLEX, but my heart can't take any higher speeds, so I wouldn't know if my engine would belch smoke if it goes over 130 kph
Anyway, I hope you find a solution to your smoke belching woes.
Does the Sedona CDRi engine have a different designation from the TDIC? I'm sure mine is a TDIC, and my registration papers say the engine is a J3.