close to purchasing a D50

[CAUTION]

so as i have been told the mighty max and D50 is the same truck. the one i might buy has 90 thousand on the odometer and 70 thousand on the engine. it was owned by an elderly couple who traveled and towed it behind an RV before my friend purchased it a year ago. anything i should look out for when looking into this? the gas gauge isnt working but he told me its not a huge deal just to fill up every 200 miles. i would love your guys input thanks alot.