"Thanks everyone, I've been relying on the gauge on the pit itself. Sounds like it is time to invest in a digital thermometer to ensure I am at the right temperature. Thanks for all the input, I'll update with the next batch (hopefully next weekend)."
The only time I have ever had "tough" ribs was when I didn't get them quite done. And that was due to a bad thermometer. Speaking of which.... I have never seen an accurate thermometer from the factory installed in the smoker. They are always off ...... I had one that was off by 54 degrees. So beat feet down to your closest kitchen supply (or Amazon.com) and get yourself a good digital thermometer. I like the Taylor remote read out. Keep the pit in the 225 to 250 range and don't keep opening the lid. After about 2 - 21/2 hours, take a look and check for the meat pull back and the bend test as mentioned above. It's a snap. Finish smoking the ribs until the tests are good. Be sure to post pictures of your great results. I'd say that your problem just about has to be smoking pit is not hot enough. Good luck!