In my girl's car (not a f-body, but bear with me) when you press the gas from a stop often times it will stumble a little before it accelerates smoothly. I was thinking this is probably a torque converter problem, and I probably need to replace it. Could it be anything else?

Her car is a 99 taurus BTW

 

More than likely a sensor under the hood, even though your not popping a check engine light you may have a faulty sensor somewheres. Either rent a scanner from an auto store or run it by a shop and pay them $30-40 to perform the scan and make sure it's not 1 of 100 sensors that are bad. FWIW my F-150 would pop a check engine light once every couple months for a second or 2 then go out, finally started ideling funny and found it was a bad throttle position sensor, replaced that, cleared codes and tried again, found 2 other things needing replaced after I fixed the inital problem LOL!! So imo it's worth scanning for piece of mind, too much crap on these new cars to point a finger on 1 thing since everything works together nowdays

 

Maybe a bad plug wire?