* Different bellhousing: The bolt pattern on the engine side (bellhousing) is different. You'd need a bellhousing compatible with both the 4L80E and your truck's engine.
* Transmission crossmember: The 4L80E is physically longer and heavier, requiring a new or modified crossmember to support it correctly.
* Driveshaft: The output shaft length is different, requiring a new or modified driveshaft.
* Wiring harness: The electrical connectors are not compatible, necessitating significant wiring modifications or a custom harness.
* Torque converter: A 4L80E torque converter will be needed, which is different in size and design from the 4L60E's.
* Possible computer reprogramming/tuning: The transmission control module (TCM) may need reprogramming to work correctly with the 4L80E.
While technically *possible* with significant fabrication and mechanical expertise, it's a very complex and costly undertaking, not a simple swap. It's generally far easier and cheaper to rebuild or replace the 4L60E.