Jefferies downgrades Valero Energy to 'hold'; shares slip

** Shares of Valero Energy VLO.N shed 1.9% to $385.80 premarket

** Jefferies downgrades rating on stock to "hold" from "buy"

** Brokerage says it "likes mgmt's strategy and capital allocation / returns," but risk-reward "supports" the rating

** "Refining cracks have surged to new highs this year (driven by diesel) due to damage to Middle Eastern refineries and ongoing disruption to Hormuz flows, Russian refinery outages and export restrictions," Jefferies says

** Up to last day's close, shares up 141.6% YTD