Fitech

Hello am new to the site...
I put the fitech go street 400hp on a 87 corvette l98 350 sb, comp hr 264 and flat tops. It does everything right except when transitioning from a coast to throttle tip in after warm up. It goes way lean 20afr and almost dies then catches up. Ive tweeked the crap out of the accel pump settings. My thought is fitech is an above the blade injector style. The fuel cant get past the closed blades as fast as the air. The holley snipers are below the blade injector style and thus the fuel is where it needs to be when slightly opening the throttle. Better response no stumble. Naturally Fi tech doesnt buy my idea. Comments?
I had the same problem with my 400 in a 68 fury with a 318. My iac was at 3-4 (which is within spec) moved it to 10-11 reset the values and problem went away