After re-installing the transmission i forgot to put the magnet back in the transmission pan?

When I put my truck I to reverse it literally takes 15-30 second to actually feel the truck go I to reverse. Why? What is causing this? I've changed the fluid filter and shift solenoid. Still does it. Help please.

The magnet is used to catch stray metal particles which can cause problems if they get by the fluid filter. The reverse shift problem can be the transmission seals for the reverse band/servo are worn out. I would try a bottle of Lucas transmission saver; my son uses it all the time and says it works great. Let me know how it goes.

I'm going to get a bottle of Lucas tomorrow and I'll let u know. Now should u use just Lucas. Like drain what's in it out then refill with Lucas or just drain a small amount out and top it off.

Also my truck taps loudly. Sometimes it doesn't but most of the time it does. It sounds like a lifter to me. I'm wondering if I can take the valve cover off and maybe tighten something down so the tapping stops.

You can just add the Lucas, it is only a small amount so you should be okay. Also, please start a new question for the tapping noise, and upload a short video to help us see what going on as well.