Transmission problems

Good evening,

From sitting that long, what have you done to get it back in service? Every fluid in the truck needs to be changed.

The transmission fluid and filter may be the only issue with the problem you have. I would change the fluid and filter as a start.

https://www.2carpros.com/articles/how-to-service-an-automatic-transmission

Roy

1. Raise and support the vehicle. Refer to Lifting and Jacking the Vehicle .
2. Remove the catalytic converter. Refer to Catalytic Converter Replacement (LL8) Catalytic Converter Replacement (LH6/LS2) .
3. Place a drain pan under the transmission oil pan.
4. Remove the oil pan drain plug, if equipped.
5. If necessary, remove the bolts and position aside the range selector cable bracket for clearance while lowering the pan. It is not necessary to remove the cable from the lever or bracket.
6. Remove the oil pan bolts from the front and sides of the pan only.
7. Loosen the rear oil pan bolts approximately 4 turns.
8. Lightly tap the oil pan with a rubber mallet in order to loosen the pan to allow the fluid to drain.

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9. Remove the remaining oil pan bolts.

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10. Remove the oil pan and the gasket.

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11. Grasp firmly while pulling down with a twisting motion in order to remove the filter.

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12. Remove the filter seal. The filter seal may be stuck in the pump. If necessary, carefully use pliers or another suitable tool to remove the seal.
13. Discard the seal.
14. Inspect the fluid color.
15. Inspect the filter. Pry the metal crimping away from the top of the filter and pull apart. The filter may contain the following evidence for root cause diagnosis:

Clutch material
Bronze slivers indicating bushing wear
Steel particles

16. Clean the transmission case and the oil pan gasket surfaces with solvent, and air dry. You must remove all traces of the old gasket material.