When driving at 25-45 the truck, it has a noticeable rock seemingly from left front to right rear. Almost as if the right rear shock is gone. The right rear lists very slightly from left to right too.

 

last year mine did that too, a friend thought I had a broken leaf. turned out to be old sticky shocks combined with the weight of a full tank of fuel making it sag towards the drivers side. Replaced the shocks and when nearly empty the truck looks and rides perfect

 

The shock on the right rear may be the issue. Thanks

 

Make sure your tires aren't cupped. I had an F150 that felt like it was going over rumble strips at 5mph, then it would even out with speed. The cause was cupped tires.

 

Shocks don't support weight, they dampen the spring's rebound....

Sounds like broken/tired springs, check the leaf pack for missing or broken spring pieces, also, the front cols will tire over time.

 

OK. Appreciate the reply.

 

Very plausible. I do haul a Lance Camper on a fairly regular basis over rough dirt trails. I do have air bags as well.

 

If the feeling you're experiencing is like the tires are egg shaped then its not uncommon. Typically the speed its felt is around 45 mph. People have chased their problem by replacing tires, shocks, mounts, wheels, etc..... I had the same problem and found it was separated rear tires. I think these trucks are far more receptive to tire condition and shape than people give credit.

 

I was also thinking maybe a tire issue....

This would make sense.

 

Yep, slipped belt would be my first guess.