Thre is no reason you can't get that thing running good with the stock computer, but you definately need more information to tune this car right.
You said the tuner "shut it off" at 4800 rpm. Do you mean he shut it off on the dyno or he set the rev limiter on the MSD? If you hit the MSD rev limiter, thats your backfire right there.
A lot of your info is unclear. You said "MSD FMU." MSD makes the ignition boost timing control. Not the FMU. The standard FMU disc is 12:1. A/F ration might have been 14:1. Either way you've got to recalibrate the FMU to match the injectors, probably with a 6:1.
Questions that need to be answered before you can go any further:
1) What is the calibration on the stock meter? Is it stock calibration or just a stock housing?
2) What fuel pumps(s) are you running.
3) Are you sure they are 30 lb injectors?
4) What is the base timing set at?