When I press the gas engine just revs there is no movement

Welcome to 2CarPros. Your description sounds like it could be something external to the transmission. The clanking you mention sounds like the parking lock trying to engage as the internal parts stop. I would probably do a quick test by putting the truck in park and with no brakes on see if you can push or pull it. If it moves in park there is a mechanical failure. Possibly a U-joint or something inside the transmission. If it doesn't move in park but still will not move under power then start checking farther. First check the transmission fluid level. You will want to see nice clean red fluid. Black or worse black with metal or grit means the transmission is probably in need of a full rebuild.

As it can be pushed in park the first area to check would be both of the front drive axles to see if one has failed. To do that you need to get the front end in the air enough to see and feel the front axles and have the tires off the ground. Then you can look and see if all of the parts of the axle turn when you move the tire. If everything moves and you can grab the axle and it doesn't have free play or obvious damage the issue is more likely internal, either a failed drive chain or a broken shaft. If one of the shafts has damage like a failed boot and you can hold the inner axle joint and the wheel turns then replacing the half shaft would repair it.
Although not your vehicle this is the same basic method to replace one.
https://www.2carpros.com/articles/replace-cv-axle