idealy yes you will want to have it tuned after the header install - typically a tune is best done after you have done all the engine mods you want - as you probably know from building hondas - basically you dont want to do a header install do a tune, and then do it all over again if you add something else
on your truck specifically we have not seen any issues when people have done the basic mods - intake, headers, and a exhaust system of sorts regarding a lean condition on the engine (which will usually throw a check engine light). You will gain more HP and Torque across the power band and yes more power can be found with a tune after.
I do suggest however if you are towing to go with a ceramic coated header over a raw stainless - probably why you are seeing cracks in the existing manifold, the excess heat that is accumlated from more load placed on the engine while you are towing your car puts more wear and tear on the factory manifolds - and this is ture for all makes GM. Ford, Dodge, Toyota, Nissan - we see alot of it at our performance center from customers that tow a boat/trailer/camper with their factory manifolds
We do offer 2 differnt types of ceramic coating on our headers - the silver ceramic would be the best way to go unless you are running a supercharger than I would go with the titanium coated headers.