Frustrated with tension on my machine...WWYD?

I have a Kenmore (19110) that I got for Mother's Day last year.  I didn't really start using it until the last 3-4 months.  I kept having tension issues, reading the manual, adjusting the tension knob, cleaning it, yadayadayada...and couldn't figure out the problem.  I finally brought it to my mom, who knows what she is doing (unlike me  ) and she said something was wrong with it and I should have it serviced.  I did and they found an issue and supposedly fixed it.  It was covered by the warranty (which expired a week later).  The machine seemed to be working great up until my last project.  I was sewing a hem on a dress and it got all wonky again at random.  I went though everything again and now I don't know what to do!!!  I feel like I should take it back to Sears again, but don't want to have to pay for repairs.  I'm so frustrated!!!!  Would you take it back again?

Hmmm. I would take it in and nicely suggest that the repair should have lasted more than a month . . . See if you can get them to fix it again for free or at a reduced charge. Good luck.

I totally agree - any repair should last more than one project.