Tires almost rubbing on F350 Dually when hitched

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Hello,

Just purchased a 2003 Montana 3760 in excellent condition. On the initial pull home, I noticed my tires in back were almost touching with maybe a quarter of inch or less of space between the tires. The original owner of my truck installed 235/85/16 tires which are a little over size. I am running 60lbs of air in the tires. My question, can this problem be alleviated by running 80lbs of air or is that abnormal when towing and will generate a harsh ride. Or should I just go back to stock tires? My current tires have good tread but the last thing I want to induce is a blowout. Please advise.

Thanks

Robert