If you aren't already you need to be data logging your current setup so you can check out whats going on e.g. spark, VE tables.

A seperate wide band O2 sensor will allow you to get an idea of your W.O.T Air fuel ratio is.
13.5 PSI with stock 61 lb/hr injectors sounds a bit on the light side to supply enough fuel for a 383 at W.O.T. (a healthy stock TBI 350 would push that)
Assuming you have everything like spark and VE table close to where they need to be have a look at your Injector DC% in tunerPro, if it get's to 50% then you will be running out of fuel because the injectors will be working too hard.
Have a read of this: http://www.gearhead-efi.com/Fuel-Inj...ighlight=Kitch
I use an Innovate LM1 and I mounted the gauge so I can see it while I drive and I eventually managed to get it connected to my Moates APU1 which allows it to stream the wideband O2 data into TunerPro so I can log the data rather than just look at the dash mounted gauge.

The factory air cleaner is very restrictive above 3500RPM and if your still using that it will be holding you back. If you are using it at the very least look at flipping the lid on it but only once you've checked the Injector DC% and wideband AFR as more airflow may only make your problem worse. Assuming everything else is okay you should see a change in the W.O.T MAP values at high RPM with the lid flip on a stock air cleaner.

Are you still running EGR with the 3074?