Still Surging and Bogging: What do I check next?

[BTR]

2005 RXT 4-TEC 215HP 188 hours. Surging and bogging throughout the entire throttle range. Fuel tank has been drained, both fuel filters (2) have been replaced, and fresh high-test gasoline is being used. It's still surging and bogging. Next, new spark plugs will be installed. My question is: If it still surges and bogs after new spark plugs are installed, then what do I look at next in order to resolve the problem? Thanks for your help.

 

[LakesideRec]

With that many hours, the supercharger might need a rebuild (but that would only explain the high end of the throttle range).

 

[ski-d00]

sounds like throttle body problem, idle bypass valve

check intercooler as well