What would cause your Dodge truck to shake when you get 45 mph but once go above 55 it stops if already replaced spark plugs wires cap rotor throttle body?

Here are some potential causes for a Dodge truck shaking at 45 mph but not at higher speeds, even after replacing spark plugs, wires, cap, rotor, and throttle body:

1. Driveline Imbalance: Incorrectly balanced driveshaft or U-joints can cause vibrations at specific speeds, which may disappear at higher speeds due to increased angular momentum.
2. Damaged or Worn Motor Mounts: Worn-out or broken engine mounts can allow excessive engine movement, resulting in shaking or vibration at certain RPM ranges. Check the condition and security of the engine mounts.
3. Issues with Wheel Balance or Alignment: Improperly balanced or misaligned wheels can lead to vibration while driving, especially at specific speeds. Have your wheels balanced and alignment checked by a professional.
4. Transmission Problems: A malfunctioning transmission, such as worn-out gears or torque converter issues, can cause vibration or shuddering at certain speeds. If the shaking is felt consistently at a specific speed, it may be related to a transmission issue.
5. Defective Wheel Bearing: A worn-out or damaged wheel bearing can produce a rhythmic vibration or humming noise while driving. Check for any play in the wheel by lifting and shaking it.
6. Loose or Damaged Steering Components: Worn or damaged steering components such as tie rods, ball joints, or control arms can cause shaking or vibration while driving, especially at higher speeds.

If you have addressed the ignition components and the problem persists, it's recommended to have your truck inspected by a qualified mechanic who can properly diagnose the exact cause of the shaking issue and provide the necessary repairs.