Sounds very much like retarded timing.It seems sluggish and doesn't want to pull its own weight the chargers spool quick but doesn't seem like the fuel is there
I ran mine at 19 deg. Used the same timing till i went up to a 13mm pump. Went to 21 deg with it for daily driving and towing at the 900-1000 hp level. 19 deg with an 887 pump at around 700 hp was a nice set up as was 19 deg with the 13mm pump at a bit over 800 hp.
I lost a little on the bottom with higher timing. Noticed mostly trying to run in overdrive below 70mph. That was the first thing I noticed with the 6.7 was that 70 in od was fine.