the bear II wrote:
You may be close to a U-Joint failure or a dry U-Joint. The change in angle aggravated the failing U-Joint and you get the shudder. This happened on one of our trips. Quick change of the U-Joint and the shudder went away.
My first thought is that is a failing u-joint or bearing. If both are fine, it is the drive line angle when you are loaded.
Moving the weight farther back in the RV so you have less squat with the same amount of weight will tell you if it is an angle issue. Bags or helper springs will correct this without changing your unloaded angle.