4900ex Rough ride

Got an 07 4900 that used to ride like a Cadillac. Last winter I started noticing smaller bumps getting bigger. Now when I see a decent bump in the road I cringe, which seems to be every 5-10 seconds. I've had all 3 axles gone through and ride height checked on steer, drives and cab. Replaced all 10 shocks, worn airbags replaced, spring bushings replaced, leveling valves replaced. Replaced steer tires. Drive tires are still in good shape minus a minor cup on one. The roughness travels throughout the entire truck, but I can time the bumps and am certain it's coming from both drive axles. The bumps are jarring almost to the point of my drinks in my cup holder ending up on my dash. Rough roads are completely unbearable and rattle the whole truck apart. I have been having other issues with leaks, wiring issues and loose/broken bolts and parts due to how bad the ride is as well. Anyone else experience this and find the solution?

 

I have visually checked the front cab mounts and used a long pipe to try to lift on front of cab to check for movement. The air springs were replaced about 2 years ago when one failed. When I can see a bump in the road I can feel the front end softly hit the bump, then feel the drive axles practically slam into it like the bump grew 10 times larger after the steer axle hit it. I would think if it was the front cab mounts I would be feeling the same with the front suspension also.

 

Ok, one thing I have noticed is that the rear suspension height control valve seems to release air very slowly to lower the suspension back down compared to when it raises. I can come to a stop,set the brakes, turn the truck off and do whatever for a minute or two, and by time I get out of the truck I can usually still hear it lowering the suspension a little. But it does stop after a few minutes. Valve has been replaced once already, but maybe it's the wrong part or faulty part out of the box? I do know some valves tend to dump air faster than others. I don't believe the valve for the cab suspension to be bad. I can manually operate it and see that it is functioning flawlessly and very responsive. I will have the shop back home take a look at the cab mount bushings when I get back there next, but they honestly don't look very aged. Could have been replaced before I bought the truck.

 

Update.. cab mounts have been inspected again and confirmed to be in good shape. Drive axle bushings have been inspected and are good. Torsion bars on both axles each had a bushing that was rotting so I replaced them. All airbags are within 2 years old and appear to be in good shape.
What boggles my mind now is that I made a run from Wisconsin to Florida last week and it all of a sudden rode like a dream the whole way to Florida. Unloaded, reloaded and started heading back to Wisconsin. About time I got to Atlanta it started riding rough again. So now I know it's not just my imagination thinking it's riding rough. But I can't for the life of me figure out what would cause it to ride fine for a while and then act up again. I didn't move the 5th wheel position or anything either, so that's not it.

 

Also, control valve has been replaced. No change.