US Cash Products-Selling pressure moves Chicago diffs down

* Chicago gasoline and diesel markets weaken * Harbor jet fuel jumps on airline buying * Gulf conventional gasoline slides after pipe scheduling NEW YORK, May 1 (Reuters) - Chicago cash gasoline and diesel trade lost steam and traded lower on Tuesday as the market corrected for Monday's overheated trading that led to leaps in refined product values. Chicago gasoline fell 2.50 cents a gallon to 4.00/2.00 cents under the June RBOB gasoline futures contract on the New York Mercant