Check my cardomain page. I talk about it there. There's an index at the top.
Now, warning: on a 4.0 the MAF mod can put the curve so far off you will have problems, particularly at wide open throttle. I've been able to tune that out on some by feathering the leading edge of the sense tube -- but it's not guaranteed.
Now, if you have a SCT 9415 (newer Xcal2) or an older one with the Extreme Tune software, you can define a new MAF curve. Basically, you just correct the curve at idle, part throttle, and full throttle and the software draws a "perfect" curve through that.
The 3.0 engines usually have no problems with this -- but lots of 4.0's run lean after modifying the MAF.