Tire Pressure
I'm not familiar with your trailer's brand of tires but the trailer does weigh 5000 pounds, resulting in a load of 1350 pounds per tire. A saftey factor of 20% would be wise indicating a requirement for 1620 pounds load per tire as a requirement.
Safety margins are wise because trailers are never equally loaded from side to side due to the trailer itself and equally due to road conditions, slopeing roads, bumps, etcetera.
I use Goodyear Marathons and in your size range 50 pounds of pressure would provide a load capacity of 1820 pounds of capacity per tire. As a result I would guess that you need 45-50 pounds pressure. I would suggest that you enter the full name of your tires and look for the inflation chart.
If you list the tire manufacuter I would be glad to help.
Good luck,
Norm Milliard