Here are the likely culprits:
* Internal Transmission/Transfer Case Pressure: This is the most probable cause. Something is forcing excessive pressure inside. Possible reasons include:
* Overfilled Transmission/Transfer Case: This is the simplest possibility. Too much fluid has nowhere to go when the fluid heats up and expands.
* Failing Transmission Pump: A failing pump can create excessive pressure.
* Internal Transmission/Transfer Case Leak: A leak that isn't externally visible may cause pressure to build up. This could be a seal failure, cracked case, or other internal damage.
* Clogged lines or passages: Restricted flow can cause pressure build up.
* Incorrect fluid: Using the wrong type of fluid can lead to internal damage and pressure buildup.
* Breather Tube Restriction (Less Likely): While less probable, a severely clogged breather tube *could* contribute to the issue, but it wouldn't be the root cause. The pressure would still be building up due to one of the problems listed above; the restriction only exacerbates the problem.
What to do:
1. Don't drive the truck: Continuing to drive it could cause significant further damage to your transmission and transfer case.
2. Check the transmission and transfer case fluid levels: Are they overfilled? If so, drain some fluid to the correct level (refer to your owner's manual).
3. Inspect the breather tube: Make sure it isn't kinked or completely blocked. However, cleaning it is only a temporary fix; addressing the root cause is crucial.
4. Professional Diagnosis: Take your truck to a qualified mechanic specializing in transmissions and transfer cases. They have the tools and expertise to diagnose the underlying problem and repair it properly. This is not a DIY repair unless you have extensive experience with transmissions.
Ignoring this problem will almost certainly lead to complete transmission/transfer case failure, resulting in a very costly repair. Get it checked immediately.
