The computer in your car watches numerous sensors and switches throughout the vehicle. There is a sensor that measures slippage in the transmission and will "see" the slip long before you can feel it. This is what is happening in your transmission. Here are your options:
1. You can keep driving it till the torque converter fails all the way or debris or metal from it causes another part to fail, then the trans will act strangely or stop moving and you will have to fix it. But be aware that as more particles come out of the converter or clutches begin to overstress because of the slipping converter it will increase the damage in the trans and make a repair more costly.
2. You can have the transmission repaired now and hopefully not cause any more damage, which could save you some money.
ASE Certified Technician
20 years auto repair experience, ASE Master Tech, Mechanical Failure consultant, Expert Witness