Have you tried throwing in some turns while trolling? See if you get any hits from rods on the inside or outside of the turn?
I use a moor sub troll, and the speeds we get at depth are not that much different compared to what the gps says. But we are over here in Mexico Bay, maybe our currents aren't as bad as yours out west.
We were out all day yesterday, water temps were pretty warm all the way down to 120', Salmon bite was non existent. marked alot of fish in 190 FOW but had no cooperation.
Came in to 90' and had some good luck with the browns.