Why is my truck riding so rough?

My 1993 Peterbilt 379 EXHD has always rode rough. I think Peterbilt started making the cab/sleeper air ride in 1994. So sounds like I missed it by a year. But this is a long wheel base tractor and it seems like it should ride a little smoother. I haul grain off the farm during the harvest season with a hopper bottom trailer. Some people has said my fifth wheel may be set wrong. Its set so the front of the trailer is in the middle of the front axle tires (when looking at it from the side). Some have said I may need new spring eye bushings or torque bar bushings. I've looked at the spring eye bushings and can't really see anything but grease. The torque bar bushings don't look completely worn and the inspector didn't mention them when the truck was inspected a month ago. When I get on a certain road for my routine haul, it almost throws me out of the seat. Its a very rough road that has been needing to be repaved for about 10 years and they keep patching it in places which makes it even worse seems like. I've adjusted the leveling valve to where my trucking buddy said it needed to be. It was adjusted wrong when I first bought the truck so I thought that'd help and it did, "some". The truck has the short style air bags which probably isn't the best. Wonder if they could be swapped out for big ones? The truck feels every little bump in the road and on a rough road, I think I'm going to hit my head on the headliner. Does anyone know what the problem is? This is a Peterbilt 379...aren't they known for their smooth ride? Even the older ones???

 

Baha, the driver's seat is a good seat. Its a Bostrom WideRide. I can tell the bounce is in the truck because the truck as a whole starts bouncing before the seat does. Its a straight up and down bounce which is usually worse loaded...and when I come to, for example, a road/bridge joint, it sounds like the back axles are going to break off; loaded OR unloaded. Jbatmick, tire pressure is about 100 lbs and I've ran it differently before. The inspector was actually my father in law who is a trained diesel mechanic, and he also is an inspector. He actually told me the sway bar needed replacing on my OTHER truck that he inspected, a 95' International 9400 Eagle. So obviously he looked at the bushings on the Pete. He also said the shocks needed replacing on one of my trailers he inspected so I can't figure out why nothing was mentioned about the Peterbilt. I'm surprised nothing was wrong with its suspension because something surely is. The road I notice it on is in horrible shape but I notice semi trucks behind me and I'm driving slower than they are. Something can't be right.

 

Bavarian, yes your probably right that they only look at shocks to see if they "look" good because my father in law said one was broke on the trailer and not even attached on one end. I haven't noticed any uneven tire wear. I just had a new rear end put in this truck and it was in a good, trusted shop. They said the U joints in the drive shaft had a lot of slack in them. They tightened that up for me too. I just wonder if traveling that rough road without good shocks done that. I just don't want to screw this new rear end up because of a rough ride. I've heard China tires can cause a ride like this and the truck has Sailun tires on it (made in china). I'm definitely going to look in to new shocks. Anyone driven an older Pete 379 like this? 93 and older? How did it ride with good shocks? I'm anxious to see for myself.....