Need advice for Pete 387, 2003

I have 2003 Pete 387. It is viberating during driving while empty or loaded both times with trailer and bobtail. I got it checked from everywhere but nobody could find the problem. It has everything new from Transmissio,Rear end , New bushing,New U-Joints and new Leveler Valve. It starts viberation sometimes not all the time mostly at 55 to 60 mph. And i also start feeling it is not riding on air suspension. One of the mechanic told me yous middle axle is viberating during driving and he also said he feel like it is riding on spring suspension. He said your trucks air regulater valve is bad. I ask him to replace it he said he cannot find it and you may need to go to dealer. Then i go to dealer he said there is no that kind of valve is in your truck except leveler vave. Anybody has any suggestion or advice it will be very helpfull for me.

 

I already changed all of shocks and got checked ball bearings and torqued hubs

 

I also got my driveline checked and balanced.