I've got TTS dual lift pumps and I don't know whether they are running or not.

I recently logged some data, and on long pulls my rail pressure drops off from the commanded by varying amounts.

I do run quite a bit of fuel, but I didn't think my rail pressure was falling behind much.

Whats the best/easiest way to check and see if these things are working?

Only thing I can think of is throwing in a gauge after the filter housing. Or is before the filter housing best?

You can purchase a Kennedy diesel fuel pressure gauge and check them that way.

ya a pressure guage will be the easiest way to find out