Had the same problem with my '05 Sport, Blower Motor Resistor. It's kind of a pain to get to, but there's some good write-ups out there. I just pulled the passenger seat to lay on my back while I was working on it.
We carry the resistors they should be back in stock soon.Wasn't sure if you needed one but here's a link to them on our site. Jeep Heater Blower Resistor