LT225/75R16-D is rated at 2,335lbs at 65psi or 4,670lbs GAWR
LT225/75R16-E is rated at 2,680lbs at 80psi or 5,360lbs GAWR
Given that the original poster listed his GAWR=3600 front, 4670 rear, D's will do the job.
But going with the E is definitely an added measure of safety and will improve...