Is it true that at WOT the computer does not have control of the injectors and that fuel pressure is in more control?

 

No, the ECM always controls the Injector Pulse Width. What happens is the ECM does not make "fuel corrections" based on the O2 sensor when in WOT - it relies solely on the tabels within the ECM and the other sensor readings.

 

So It is important to get a aftermarket chip or burn one to get the full potential of your engine even when you raise the fuel pressure right?

 

Aftermarket chips are generally too rich as is. It is best to tune the eprom to the specific pressure you wish to run. This requires "hands on" tuning and monitoring - not an eprom "off-the-shelf, by mail or burnt-by-specification". Raising fuel pressure does not behave in a direct "linear relationship". It has it's greatest effect in WOT and least effect at low load/part-throttle. So you generally adjust only part of the fuel tables.