If I tweak my rig, 96 FSB 5.8l EFI, say with some aftermarket heads, do I need to swap out the fuel injectors, as a rule. I understand the heads may fiddle with my ECM, so, if I do one mod, the heads, then is it a domino effect: injectors, plug wires, etc....? wouldn't upgraded injectors need an fule pressure guage of some sort?

 

No, the stock injectors are good to about 275 to 300hp with the proper fuel pressure.
If the truck has MAF, then the heads will not effect the ECM.