I agree those bags look far overextended. No way you should see the joint of the bag to the base sitting there at normal ride height (assuming the pic was taken at ride height). when it is stretched all the way out like that the rear has no down travel. In general terms, it should be midway through it's range of travel so the rear can go through normal up/down travel. If you have the part number for the bag the manufacturer catalog will tell you the correct installed height (at rest) as well as the max extended and compressed lengths.
My suspicion is the previous owner has the suspension overextended via air pressure or leveling valve position to make the ride height somewhat higher than it should be either to "look" level with a full bed, or to get a certain hitch height. Which would explain a drivetrain vibration, all the angles would be out of wack at full extension like that, but would not explain why it changed. While the air bad being at an angle is not good as it will increase wear on the rubber sleeve as it moves, it really shouldn't affect drivetrain angles or vibration.
