[nissanfanatic]

Its probably leaning out at 6k because voltage to the fuel pump is dropping. Or you may still have the stock pump(which isn't a bright idea at all).

How are you sure its running rich? BTW, running really rich isn't safe either. Too much fuel washes oil off the cylinder walls causing increased cylinder wear.

Check for a boost leak.

And list your mods please. Its hard to know whats wrong when you don't know what it is....