There is a thread running over on the HAMB right now about rust removal and the different types of converters guy's have used. I found a Phosphoric acid based product is one of the most common and least aggressive on the metal but there are all kinds for all types I guess.
It may be the easiest way to go for your situation but be warned depending on what type of primer you use you can run into adhesion problems if the acid is not neutralized and dealt with properly.
I see the plus side being you can get it into the pitted area where a wire wheel or grinder won't reach. Neutralizing the acid while it's still wet is key. So if you follow the directions and let it dry, then sand/wire wheel the residue off then reapply and while still wet wash with plenty of water you should be safe. Plenty of guys just sand off the residue or even leave it and then apply their rustoleum or what ever but with certain brands of Epoxy that is asking for trouble down the road unless the 'while still wet' neutralizing takes place.
The nice thing I found with the epoxy is I can just keep laying it on and filling those pits until everything is smooth. It also is water proof and it also encapsulates and bits you may have missed (I found its cheaper than Por-15 to boot).

In the end it sort of depends on your intentions for the truck as to how deep down the hole you want to go....


Give me ambiguity
or give me something else