Most Likely Causes:
* Driveshaft: This is a frequent cause of vibrations in that speed range. A worn or unbalanced driveshaft can cause significant vibration. Look for signs of damage, bends, or rust.
* U-joints: These connect the driveshaft to the transmission and rear axle. Worn U-joints are a common source of vibration, especially at higher speeds. Listen for clicking noises, especially when turning.
* Wheel Balancing: Unbalanced wheels are a very common cause of vibrations. This is a relatively inexpensive check and should be done first.
* Tires: Worn, cupped, or improperly inflated tires can also cause vibrations. Inspect your tires for uneven wear or damage.
* Axle Bearings: Worn wheel bearings can cause vibrations that worsen with speed. You might hear a humming or grinding noise along with the vibration.
* Transmission Problems: While less likely to cause vibration only in that specific speed range, transmission issues can contribute to vibrations.
* Torque Converter (Automatic Transmission): A failing torque converter can produce vibrations, but usually across a broader speed range.
Less Likely, but Possible Causes:
* Engine Misfire: While less common to manifest only at that speed, a misfire can contribute to vibrations.
* Steering Components: While unlikely to cause vibration specifically in that speed range, worn tie rod ends or ball joints can introduce vibration, but usually more noticeable at lower speeds or during turning.
* Body Mount Issues: Worn or damaged body mounts can allow more engine vibration to transfer to the cab.
Troubleshooting Steps:
1. Start with the simplest and cheapest: Check tire pressure, inspect tires for wear, and get a wheel balancing done. This is the most cost-effective first step.
2. Listen carefully: Pay attention to any accompanying noises (clicking, humming, grinding) to help narrow down the problem.
3. Visual Inspection: Carefully inspect the driveshaft, U-joints, and suspension components for any visible damage or wear.
4. Professional Inspection: If the above steps don't reveal the problem, take your truck to a qualified mechanic. They have the tools and experience to diagnose the issue accurately and safely. Mention the specific speed range where the vibration occurs.
Important Note: Driving with a significant vibration can damage other components. It's best to address the issue promptly. Don't continue driving the vehicle if the vibration is severe or accompanied by unusual noises.
