We only run snaps to our crankbaits.We feel that the snap provides more action to the lure than a swivel. Since you were going less tham 1.8mph, the speed most likely was not causing your twisting issues. You did say that you do tune your cranks.We do also tune ours when i first put them out to make sure running straight.What can happen sometimes, when you put the crank out,the line could get stuck on a treble.So make sure that the lure is running correctly when you put it in the water.It is also possible a fish strike could cause the line to get stuck on a treble.That would surely cause the line and lure to twist.As for leaders with cranks,most of the best fishermen agree that leaders are not necessary trolling cranks.They say can run a hi vis braid straight to crank and catches same as flourocarbon.