Here are a couple things to keep in mind. Tow ratings/GCWR is rarely the limit for RVing with a half ton. Receiver, payload, rear axle are typically exceeded well below tow ratings when you load a family, a bed full ot camping gear, and 900+ pounds of tongue weight. Take a look at the Tire and Loading sticker for as equipped payload as it varies from 800-3000 pounds for F150s. There are not many happy half ton drivers towing 8k loaded RVs. 7000 and under seem a lot happier.
Axle ratio is less important with 6+ speed transmissions.