1 suggestion and 1 question.
Open the IMRC box and check under the circuit board to see if you have anything caught in your geartrain. It isn't unheard of for the straight end of one of the little springs in there to break and jam things up. (Mine was broken but was stuck to the motor magnets.)
If you upgrade to a MAF calibrated for a large engine (and more airflow) - won't you get a lower Vout for a given flow, causing your car PCM to convert to a lower flow number? If 5 volts out correlates to like 600cfm on the big MAF, and you get 5 volts out from say 300 cfm on the stocker, wouldn't 300 cfm on the big one give you like 2.5 volts? Obiously these are garbage numbers - but you could do a side by each of the two mafs. Say rev to 3000 rpm in neutral and compare measured #/min for each MAF to see how different they are. I really have no idea if that's really how the MAF works - but most sensors just give a set Vout for a given measured signal - and all the conversions / calibrations are on the mesurement tool side.
