3rd Gen Ram Tech2002-2008 Rams: This section is for TECHNICAL discussions only, that involve the 2002 through 2008 Rams Rams. For any non-tech discussions, please direct your attention to the "General discussion/NON-tech" sub sections.
If you have nice wheels and are NOT using those ugly outside wheel weights but instead the cleaner sleeker sticky wheel weights....then your wheels will never be perfectly balanced and will show their true colors at highway speeds.
Also, wide rims 9" and wider with as much of a positive offset as these trucks use can bend very easily. a slightly bend could amplify on the highway. You may not see the bend or think you have one. Only way is to put on a tire machine and eyeball the edge of the wheel. Even a well balanced combo can still vibrate under high speeds. Especially a well balanced slightly bent wheel.
Bad tires with slipped belts can too. Sometimes the belts can slip from the inside and still appear to be fine on the outside.
Lastly, tierod ends can cause the same wobble issue. My truck had a wobble every now and again on the highway. When I pulled over and stopped and took off again it would be gone. The rhythmic motion wouldn't stop unless I slowed down enough. My outer tierod end on one side and inner on the other were bad. Very low mileage btw. Probably not what you have just worth mentioning.
Not absolutely sure, Ive installed Rancho shocks, front and back, removed front driveshaft for the 4 wheel drive. Most recent info Ive gotten is that my truck doesnt have the factory driveshaft. An aluminum driveshaft, I have a steel one piece shaft on my QC. Not sure if thats right or wrong.