Engine? on 2004 Buick Rendezvous

I have a 2004 Rendezvous, yesterday I was driving and started losing engine power going uphill, This morning I changed the oil which needed to be changed, I took it for a test drive and it seemed the problem had gone away, 1 hour later as I was driving it did it again, I could only do about 35 MPH going uphill, will this be an engine, transmission problem? or changing the air filter will solve it, Please Help!!!

Asked by for the 2004 Buick Rendezvous
2 answers 1 comment
Another possibility is a failing fuel pump, unable to provide sufficient fuel pressure or volume. Is there a Check Engine Light/Service Engine soon light on? If so codes stored in the computer of your car may indicate where the problem is.
I have no lights whatsoever and it only does it now if I press the acelerator too hard if I go easy on it I have no problem and can do about 70 MPH
sounds like a clogged cat converter . a shop can do a snap throttle test with a vacuum gauge to confirm.