Jim, you might consider trying a Shuttlehawk....
https://www.youtube.com/watch?v=g4DoOpcp8uw this device really works.
The amount of drag underwater is also related to the size of your lures.......I fish a 4" or 5" quickfish/flatfish any where from 25' to 120' depth with a 4.25# weight.
I agree that after 6 miles, your legs get very tired and I am trolling in the 1.6 to 1.8 mph range.....its a real workout!
If your lures offer less drag, that's a plus, but I have found the larger, active lures tend to catch the larger fish.
Good luck!