I'd be looking at your converter. Was it matched to the rest of the combo or does it just slip?
My 400 has the same size cam (
[email protected]), RPM intake, 750 vac holley, 1 3/4 headers, 2.5" with X all the way to the back, 5 speed toyota gearbox and 3.5:1 rear gear and it absolute obliterates the tires on demand.
Re: the aircleaner, I run a K&N Extreme lid with a 2 3/16" x 11" element.