When my RPM's get up there I get a rattle going on from underneath. Not sure what that is. Rattle/Vibration becoming more pronounced. Thanks guys I am sure you know what it is.

 

Well without you having your signature filled out to let us know what engine you have............
I'll guess that if its a V-10 or 5.4 that it could be the torque convertor cover on the bottom of the bell housing or a loose heat shield on the exhaust around the Y (T) pipe. Those are the two most common RPM related rattles on the gas rigs.
For a loose heat shield you could either remove it or wrap it with a hose clamp to rescuer it to stop the rattle. For the TC cover, remove it and give it a slight twist, then reinstall.

 

If you suspect the heat shield you can get underneath and tap on the exhaust in different points with either your hand or softly with a rubber mallet. If you hear the rattle, have a buddy hold the different heat shields until the rattle goes away and clamp that one. I had 2 that were rattling but they aren't any more thanks to some 50 cent hose clamps!