How do I lessen the effects of thickening caused by roux? I recently made slow roasted pork shoulder in the oven. I cooked the pork at 225F for 12 hours and after it was done roasting, I took the juices at the bottom of the pan and made gravy with it. 

I did this by chilling the juices for a little while, and skimming the fat off the top. I got about 1.5 tbsp of fat out of that. I combined an additional 1 tbsp of butter and 2.5 tbsp of flour into it and cooked it until it was a dark brown. Then I added the juices into the roux along with some stock. 

At first I tried the gravy and it tasted magnificent. Great mouth feel and concentrated meat flavor. But I noticed that it got thicker and thicker. So I added more stock into the gravy to thin it down. Eventually I got it to the thickness I liked by adding more stock. But tasting the gravy again, it had nowhere near the glory it had before the addition of stock.

Note that I don't really want answers that focuses on the pork roast or gravy making aspect. I only added that information as background information. I'm not too interested in fixing the already diluted gravy I have. I'm more interested in knowing if I could have done something else originally to lessen the thickening caused by the roux in my gravy.
I believe that rather than "diluting" your gravy with stock, you could instead use less roux (fat and flour) with the same amount of juices (and perhaps a bit of stock).

The extra tablespoon of butter, for example, meant you were "bumping up" the thickness of your final gravy to the next level. Here's some typical ratios from an earlier Question I had about what makes a white sauce "medium":


  Medium refers to the thickness level of the final sauce, and is
  controlled by the ratio of roux (butter/flour) to [liquid]. For 1 cup of
  [liquid]:
  
  thin = 1 tablespoon each flour/butter
  medium = 2 tablespoons each flour/butter
  thick = 3 tablespoons each flour/butter


So instead of using 2.5 tablespoons of fat and 2.5 tablespoons of flour, you could leave out the butter; a 1.5/1.5 tablespoon roux with the same volume of liquid might give you a texture closer to what you're hoping for.