Thanks to all for responding.
I don't think it's as serious as a tranny slipping(certainly hope not). The idle is about 600rpm, the W/S switch is in the S position. I think tkamiya is right as the car has a very stiff gas pedal.
Per Mr. haasman, I checked the throttle linkage (I believe it's at the other end connection to the gas pedal?), I notice that the spring is quite stiff so that maybe the case. I am not sure how to adjust the cable or lubricate it?
Mr. beevly & Kestas, I wander if you have felt a difference in "feathering" a Japanese's car? (say Honda accord, Nissan Maxima something of a V6). To me, it just seem much easier. Maybe, it's something that I need to get use to.