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Hello and thank you for your question,As long as you only put one gallon of gas in the tank and you have 38 gallons of diesel you should be fine, one gallon diluted with this much diesel will not cause any harm and or adverse affect. The fuel filter should not be affected as well with such a little amount. You have plenty of diesel fuel to give the engine the lubrication it needs.
To be on the safe side its would be a good idea to add one quart of ATF (transmission) fluid to the tank as well to assure you have enough lubrication in the fuel.