Hi 72daywmn,

Using these two together usually isn't recommended unless specifically instructed by your doctor. More likely than not, it's the ibuprofen that is causing the stomach upset. In any case, no more than 4000 mg of tylenol should be taken within a 24 hr period, and no more than 1000 mg within any 6 hr period (including any that is part of a combination drug like vicoden or percocet). If taken long-term (longer than 2 weeks) the daily maximum is 2600 mg within a 24 hr period. Be sure to check the strength of tylenol you're taking; regular is 325 mg, but extra-strength is 500 mg.

In any case, if taking that much tylenol on a regular basis, it is recommended that you start taking NAC (N-acetyl cysteine) on a regular basis, 750 mg twice a day for as long as you are taking those doses of tylenol, to prevent liver damage
http://yarchive.net/med/tylenol.html

If you develop any severe stomach cramping or rectal bleeding (sorry) discontinue the ibuprofen IMMEDIATELY (voice of experience) and call your doctor.

Doc