[Dead Parrot]

As a daily driver, how many parking lot speed bumps do you have to deal with? Unless you go very slow over those, the truck will want to bounce a bit as the tires get to the flat road after the bump. About the same time as your headers are over the bump. If your truck is heavily loaded, it will both be sitting lower and subject to more bounce.

You might want to consider some shorty type headers first, then see where you are on being able to lower things. Otherwise, you might wind up re-buying lowering stuff if you buy lowering stuff first, then change the headers.