losing rpms

[Dhingle]

I have a twin 2007 250's on my 33 world cat. for the past couple of months my port engine has been running "rough at high speed". when topped out it will suddenly drop 4-500 rpms then picks back up, no rhyme or reason. no codes. changed low pressure filter, water separator, new bulb, replaced screens in injectors, tested injectors and all flowed even. I didn't change filter in vst pumps this spring and I know I need to replace fuel lines this fall. any suggestions where else I may need to look? I am changing vst and high pressure filters tomorrow.

thanks