* Gulf Coast gasoline down 1.25 cents/gallon * Gulf Coast ULSD down a cent cents/gallon * Chicago gasoline down 2.00 cents/gallon * Harbor gasoline slumps in pre-holiday trading NEW YORK, April 5 (Reuters) - Gulf Coast gasoline and ultra-low sulfur diesel differentials fell sharply on Thursday in a flurry of selling ahead of the U.S. Good Friday holiday as buyers, many of whom have already wrapped up this week's deals, left the market early, traders said. Conventional M2 gasoline differentials slipped 1.25 cents per gallon to 12.00 cents under May RBOB futures on the New York Mercantile Exchange (NYMEX), more than paring Wednesday's 0.75 cent gain on news of planned work at Exxon Mobil Corp's 344,500 barrels-per-day (bpd) refinery in Beaumont, Texas. Gulf gasoline markets also shrugged off news of a few hours of planned work Thursday on a fluid catalytic cracking unit at BP Plc's 406,570 bpd refinery in Texas City, Texas. Gulf ULSD differentials fell a cent per gallon, both on pre-holiday selling and an expected decline as traders focused on a new five-day lifting cycle the day after the previous one scheduled to move on the Colonial Pipeline. In the Midwest, Chicago gasoline lost another 2.00 cents a gallon and was bid at 32.00 cents under May RBOB gasoline futures and offered at 28.00 cents under futures, as the cycle changed and two refiners continued selling, traders said. The selloff followed a weekly government report that showed Midwest refineries ran 92.3 percent of their capacity last week, compared with the 88.3 percent of capacity that was utilized in the same week last year. Differentials were also pulled lower by the crack spread between RBOB gasoline and U.S. crude futures contracts on the New York Mercantile Exchange, which had hit a record high above $40 a barrel on Wednesday but receded to $35.74 a barrel at midday on Thursday. The New York Harbor gasoline market slumped on Thursday, with all grades losing ground as traders wrapped up business before the three-day Easter holiday weekend. Prompt winter-grade F4 RBOB fell 4.00 cents a gallon to 11.25/11.75 cents under after rising by 2.00 cents earlier in the day. Prompt summer grade F2 RBOB was done at 5.00 cents over, down 2.00 cents a gallon. Prompt summer-grade M2 conventional gasoline, meanwhile, tumbled by 4.00 cents, with a deal done at 3.50 cents under. Harbor distillate markets saw prompt heating oil firm by a quarter cent to either side of 1.00 cent over the April heating oil futures contract on NYMEX. Prompt ULSD dipped by a half cent and was called 8.50/9.00 cents over in thin trade. For more refinery news, please go to U.S. GULF COAST Cycle 21 M2 gasoline was seen done at 12.00 cents under May RBOB futures, down 1.25 cents. Newly prompt Cycle 21 61-grade ultra-low sulfur diesel was seen done at 5.75 cents over the May heating oil screen, down a cent a gallon. Cycle 21 54-grade jet fuel was flat at 5.00/5.25 cents over, down about 0.80 cents a gallon. Scheduling Cycle 21 heating oil gained a quarter cent to 3.00/2.50 cents under earlier in the day but ended flat at 3.00 cents under. NEW YORK HARBOR Prompt M2 conventional gasoline was called 3.75/3.25 cents under, down 4.00 cents, while any-April material was talked at 4.75/4.25 cents under, down 1.50 cents. Prompt F4 RBOB was pegged at 11.25/10.75 cents under, down 4.00 cents, while prompt F2 RBOB was talked at 4.75/5.25 cents over, down 2.00 cents. Any-April F2 RBOB was called either side of 2.00 cents over, down 5.00 cents. Prompt heating oil was pegged at 1.25/0.75 cents under, up a quarter cent, while any-April heating oil was talked at 0.50 cent under to flat to the screen, up 0.75 cent. Prompt and any-April low sulfur diesel were called 3.00/4.00 cents over, up a quarter cent. Prompt ULSD was talked at 8.50/9.00 cents over, down a half cent, while any-April ULSD was pegged at 7.25/7.75 cents over, also up a quarter cent. Prompt and any-April jet fuel were called 8.75/9.25 cents over, up a quarter cent. Prompt and any-April kerosene were pegged at 12.25/12.75 cents over, up a penny. MIDWEST Chicago cycle 2 gasoline fell 2.00 cents a gallon and was bid at 32.00 cents under futures and offered at 28.00 cents under. Chicago cycle 2 ULSD rose a half cent to 1.00 cent a gallon to trade at even to the May heating oil futures contract. Group Three gasoline rose a cent a gallon to 21.00/19.00 cents under futures. Group ULSD was flat at 5.00 cents over futures.