I know the stock injectors for the '99 5.3 are 28#

 

Yes sir they are...00 and up are something like 24.7# for the 4.8,5.3, and 6.0. 99 was a weird year, and their either 19 or 21#, can't remember.

That's a little high, the 07+ flex injectors are in that area (not sure exactly), but 99-07 are the flow rates (or close to) that I listed above