Originally Posted by FaceDeAce

Causes of shudder to consider. These apply to under light load condition described.

- Worn or stiff universal joint. Typically the one at the rear differential. Under light load of 1/3 to 1/2 throttle. Heavy load the shudder may still be there but much less noticeable. Coasting there is nothing, usually. First step is to grease the universal joints and test drive. If shudder goes away, put universal joint replacement on your todo list. If there is no change, it may still be the u-joint but consider other points too.
- Limited slip differential clutch plates chatter. Usually at mild take off, or same in a slight turn. The chatter can happen on straight away runs if things in there are really bad. The clutch packs may be worn, burnt, warped/sticking, or the oil may be just too deteriorated for the LSD to function properly. Take out a sample of oil through the fill hole and check it. Change the rear differential oil with a quality synthetic, most good ones have LSD additive already in them. If in doubt, add it.
- Tire balance. Tires can be frustratingly weird. Slightly out of round or internal defects can give inconsistent symptoms. Examples: A flat spot from hard braking or egging from doing burnouts. An out of balance of just the right amount can cause resonance in the suspension, feeling like shudder. A harder shudder at higher speed would indicate wheel balance. A constant shimmy/shudder at a specific hold speed only would be resonance. A shimmy/shake that is momentary and disappears can be a tire defect. Inspect the tires for any bulges or uneven wear pattern. Test drive and see if you can pinpoint when it comes and goes, particularly wrt speed. Try adding air to the tires, +10 psi or reducing air -10 psi and see if the condition changes. Note if it comes back at a significantly different speed. If the condition significantly by adjusting tire pressure. Replace the tires.
- suspension resonance. Poor condition shocks or shocks that are not correct can be out of tune. The normal vibrations of the driveline can be enhanced by resonance which the shocks cannot control. Test this by adding a load to the box of the truck. Put 500lbs in the box and see if the shimmy/shudder disappears. If it is gone with the added weight, then replace the shocks.
- Transmission fluid condition, torque convertor lockup. Old transmission fluid carries some particulates in it which can make shuttle valves sticky as well as affect how the clutch plates behave. Try engaging the tow/haul OD-off button. This will prevent the transmission from engaging the torque convertor (except under really light loads). Try to replicate the shudder conditions of load/speed with the OD off and with it on. If the shudder never occurs with the OD off, then service the transmission. Simple filter and fluid changeout. There are some transmission slip/shudder additives that you can buy and pour into the transmission to help extend the fluid until you get a roundtuit. Do not be scared of them, they are safe to use. Just pick a reputable one. It is important to remind yourself that would be temporary until the fluid can be changed.
- Engine misfires. Repeating misfires almost always throw a code so will be obvious. However mild occurrences may not trigger a code. Misfires are hard to detect by the seat of the pants under light-medium load until the torque convertor lockup engages. Normally these will be dampened by the torque convertor fluid flow. When the TC lock engages, it is then direct coupled to the engine crank. At that point and that point only will you feel them. To "see" misfires you need an advanced scanner. Misfires can be a fuel supply problem, worn spark plugs, weak coil, dirty injectors. Typically the fix is to review when last spark plug change was done, and replace them. 99% of the time new plugs is the fix. No fancy schmancy spark plugs in this engine! Basic straight copper, NGK V-Power 5306.
- NB: a sticking EGR will cause misfires.
- sticking brake caliber. Takes a couple miles and the right speed to heat the rotor. Rotor warps a bit from the heat on the one side then starts grabbing. Causes shudder. When the shuddering is occurring, apply the brakes. Not lightly and not too firmly. If the shudder stays while the brake is applied and truck is slowing, then the problem is one or more of the brake assemblies.

That should about cover all of the possibilities for your consideration. As you can see, it will take you some time to think through and test/check each until you find it.

Originally Posted by Keaton E-Croteau

Originally Posted by Keaton E-Croteau

This sounds allot like my problem.

Its to cold here right now to work on my truck unfortunately but i this is going to be next on my list because of the engine light as well.

No garage and -40 Celsius is a little to cold to be working on a vehicle. haha