Charlie,
Did you soak your casings? I had one batch of tough casings on my sausage before I started to soak overnight. Since I have changed, excellent luck. I also put a splash of lime juice in the water while soaking. You could have bad casings also. I have had good luck with Butcher Packer & Syracuse Casing.
My new method for temps are 130 deg for 1 hour to dry(no smoke), 150 for 1 hour with smoke & 180 deg (with smoke) until sausage hits 152 deg. I do not go to 165. I then program smoker to drop to 140 deg if I happen to be missing for a few. Bottom rack does cook faster. This lets me finish in around 3- 3.5 hours instead of an all day deal. Just be careful you get them off when they hit temps.
Hope this helps.