The EEC Tuner is a very powerful tuning tool. However, it's best used in conjunction with a Wide band O2/data logging system. I recently bought an Innovate Motorsports LM1 and the aux. input rpm convertor. The tuner is difficult to use without any data capture for precise tuning.
I learned more regarding how my car was running in 30 minutes with the LM1 than I'd learned in 3 years with the tuner alone. Now I'm down to tuning the MAF function by +/- 1% or less at various points to get the fuel curve perfect. It can be that precise.
Buying an 'off the shelf' chip is pretty much a waste of money. Even a custom chip will need to be revised a few times to be just right. It's pretty much impossible to have a tune done remotely via mail.
The EEC will compensate for most small imperfections over time, but that still doesn't make it just right. And, every time the battery is disconnected, it will have to relearn all over again. If the fuel curve varies over time, the tunes wrong.
Good luck!