Errr....could you elaborate a bit? What truck, what drop, what components to drop truck. What is your trans problem exactly? when a truck gets dropped the driveshaft could move in slightly but not enough to damage anything. Usually the issue would be an improper driveline angle. The other possibility, depending on what truck and what components you used, aftermarket axle saddles COULD be installed backwards pushing the driveshaft forward instead of keeping it in the right spot....that could be an issue.
If you can clarify a bit I could probably be more clear.
Cameron