Biggershaft96 makes a good point. Upgrading the old csfi spider injector to the MPFI might not add much power according to the dyno but it definitely smooths out the engine and is noticeably snappier than the csfi, and more reliable by a long shot.
I have two 1999s, the C1500 Sub still has a good csfi, the K1500 Sub has the new MPFI, and you can definitely feel a difference in throttle response.
While you are at it, pull the whole intake and clean it out, put in new Felpro gaskets (only the rubber ones with metal frame).
You should have a good tight intake for a long, long time. I dread owning one of these trucks knowing it has anything other than the Felpro.
Some people claim good results upgrading the intake to the marine version but I cannot testify to that. But worth considering if you're doing the injectors