2009 DL650 acts like rev limiter kicks in at 5500 RPM

It's the most important symptom of a clogged fuel filter. If you hit the 5500 RPM with full throttle, can you coax the bike to go a bit faster with partial throttle?

Note that what's clogged is not the external strainer, but the fine filter that's internal to the pump and cannot be replaced separately.

First search this forum for "fuel flow test" and perform it. See how much fuel you get. Then, most likely, you'll want to search for the "external fuel filter mod" and perform it.

+1 with BackPacker

Not sure where you are located, an aftermarket high pressure filter cup can be purchased. Have a look at the reply #6 of '07 Fuel pump clogged....anyone tried a replacement.... It appears that motosport.com may sell the high pressure filter cup section known as a pressure regulator, plus from what I've read, it comes with a new external clip-on fuel regulator.
Edit: This is good news for those who don't want to go the fuel filter bypass route, External Fuel Filter modification

A side note, the motosport.com site may not be available to everyone, as it gives me a message "Due to GDPR regulations, MotorSport.com is no longer available in the European Union", so it would depend where in the world you find yourself.