Was towing a load shifted truck into low to take off when went to shift it stuck

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Have typical trans problem of trans cant decide what gear to be in when at low speeds had fixed twice went out again 78000 miles on truck. Now truck is stuck in low linkage is jamed in tranny???? Diconected linkage and shift lever on trans is stuck in low gear....not a 4x4 ......any ideas can i drop pan and see linkage from their ? Is tranny shot or just lemon.