If the temperature is terrible, our doctors have said that Motrin and Tylenol can be taken together. They both bring down the temperature, but they effect the system in different ways. I think they'd rather you NOT do that, but with a temp of 104, I think they'd rather treat the temp aggressively rather than let your child bake like an oven roaster. The important thing is to NEVER overdose with the same medication. That's why they say to take motrin AND tylenol, not just increasing what is already being taken. Of course, ask a doctor first.
I hope you little one feels better soon!