Most Likely Causes:
* Low Transmission Fluid: This is the absolute *first* thing to check. Low fluid can cause all sorts of shifting problems. Check the transmission fluid level with the engine running and warmed up. If it's low, add the correct type of automatic transmission fluid (ATF) specified for your truck. However, *don't overfill*. If it's significantly low and you find burnt smelling fluid, the problem could be much more serious.
* Transmission Valve Body Problems: The valve body controls the shifting. A malfunctioning valve, solenoid, or internal blockage can prevent the transmission from shifting correctly. This often requires a professional transmission repair or rebuild.
* Torque Converter Issues: While less likely to cause *only* 2nd gear, a problem with the torque converter (the device connecting the engine to the transmission) *could* contribute. This is a more involved repair.
Less Likely (but still possible) Causes:
* Shift Linkage/Cable Problems (if applicable): Older trucks sometimes use cables for shifting. A broken or adjusted cable could interfere with shifting. However, your 1999 F-250 likely uses electronic controls.
* Electrical Problems: Issues with the transmission's electrical components (sensors, solenoids, wiring) could prevent proper shifting. This requires diagnostic testing.
* Governor Problems: The governor controls shift points. A faulty governor could cause the transmission to stay in a lower gear.
* Internal Transmission Damage: Severe internal damage, such as worn clutches or bands, is possible. This usually involves a complete transmission rebuild or replacement.
What to do:
1. Check the Transmission Fluid: This is crucial and the easiest first step. If it's low or smells burnt, you have a problem.
2. Get a Professional Diagnosis: Unless you're experienced with automatic transmissions, taking your truck to a qualified mechanic or transmission specialist is highly recommended. They have the tools (scanners) to diagnose electrical issues and pinpoint the problem. They can also check fluid pressure and perform other tests to accurately identify the source of the issue.
3. Avoid Driving: Continuing to drive with the transmission stuck in 2nd gear can cause further damage and potentially leave you stranded.
Important Note: Repairing transmission problems can be expensive. Getting a professional opinion early will help you understand the extent of the damage and the cost of repair versus replacement. A rebuild might be more cost-effective than a replacement, but that depends on the specific issue.
