The 5k unit has a better trade-in value than the a 3 or 4T - better resale potential in the second hand market.
I would suggest you try a higher durometer tire first.
Secondly, watch your operators to see if the are turning the steer while while the truck is fully stopped this eats up tires. If they are the solution is to get them to turn while the truck is slowly moving when the are trying to get in position to pick or deposit a load in the storage rack area.
Just another question are your tires non marking (white) - if so the will wear out much faster as the are a softer compound tire and are they tread design or smooth (tread tires will dissipate heat better than smooth (more surface area But my inclination is that tires are being chewed up by standing still then tight turning. Like those black marks you seen in your drive way when you have turn tight because of a traffic jam.