[bry593]

Here's a video with some pointers on how to swap a 4L80E into your C10 or C20 truck.

https://www.youtube.com/watch?v=3yOop3td7Rc

If you have a C20, you probably have a 4.10 or 4.57 geared rear axle. You really can't hang with modern traffic unless you want to wind your engine up to 3000+ rpm. The 4L80E allows you to cruise 75 mph at a comfortable 2300ish rpm, reducing fuel consumption and improving usability. As an added bonus, it's a heavy duty transmission so no problem using your truck as a truck.