My current stock injectors (24 lbs/hr I suppose) are shot and I can lay hands on nice Bosch 32 lbs/hr ones as I plan to go stroker way during next winter - do I need to reprogram PCM if I install them now? Engine has following mods:

LT4 heads and intake
GMPP Hot Cam kit
BBK 58 mm TB
K&N Cold Air Intake
LT4 knock module
1LE air intake bellow
!EGR, !AIR, !TB

and PCM was reprogrammed by Fastchips (mail order).

 

The 24's are marginal with the mods you listed, and probably should have been replaced earlier. If you plan to go with a stroker in the future, make sure you buy injectors large enough to handle the HP you want to make, without running excessive duty cycle. If you plan 500 flywheel HP in the future, go with at least a 36 #/HR injector. 32's would only be a good choice it you planned to run no more than 450 flywheel HP.

Any changes to the injector size or the fuel pressure require that the new injector flow constant be programmed into the PCM. Injector offsets also need to be programmed when you change injectors.

 

Miracles happen! As I got those 32's almost for free and there is still whole summer ahead I swapped them and before sending computer for reprogramming thought to start the car and see how bad it is. And guess what - ir runs absolutely smooth, power is just outstanding, engine runs very good by sound of it and after doing 200 miles on combined city/highway I got 12.5 mpg and I was pressing pedal down very hard in city. Have no idea how to explain it, injectors were rated by Bosch 31.9lbh at 3 atm pressure.