well alot of folks have had bad mafs, if you use store brand or reman'd. i changed one on my inlaws lesabre that had a code for it. the code went out but it still ran like crap for a quite a while but since it read good on the scanner and cleared the code i thought it was good. turns out not, bought a good quality one and it has ran perfect ever since.
I got to ask this: Is the lack of the CAT, the correct muffler, and generally cobbled exhaust possibly an issue? I am wondering if the lack of back pressure could be a factor. I have done a few things under the hood and it will idle, etc. But it seems to hiccup now and then with acceleration.