How bad is my transmission?

What is your question?

for a while, my car has been sluggish when going from a stop. The rpms would cut off and slow the car down. Then lst night it wouldnt go past 15mph or 2500 rpm. I had to pull over and call a tow but then after sitting idle for some time, the rpms would act normally and I was able to get home. I think it is the transmission am I correct and what should I have looked at?