Do-it-yourself ECM/PCM Reprogramming (OBDI & II)
If you decide to get into programming for yourself, there are a few questions you need to ask yourself. First, you need to ask yourself if you are planning on keeping your current powertrain configuration. If you don't plan on making any other changes to your vehicle, it would probably be less expensive to let someone program your computer or chip. The obvious reason here is cost. Should you be one of those "hands-on" type of people, or your powertrain is constantly changing or being upgraded, then doing your own programming would probably be the least-expensive alternative. Below are a couple of links of good technical articles that explain the basics of tuning a vehicle computer as well as what special tools and equipment are required to do the job.
To reprogram most GM OBD-1 chips, you will require appropriate tuning software.
You will also need an EPROM programmer and/or UV eraser
For those of you using the 94 and later LT1 engines with the flashable PCMs, you will only require software from TunerCat or LT1edit as well as an interface cable. The 'ALDL' cables be purchased online from other vendors for as little as $50 or you can build your own for less than $20.
NOTE: OBDII Vehicles are not currently supported by every editor.
I use the one above personally and it works great on OBDI LT1, TBI, and TPI vehicles.
Most laptops running on battery power may not have enough internal power for the adapter. Or the power supply may be too noisy for stable communications. I have found this to be the case with some PCs or laptops which is why I use this design.
OBDII (1996-up)
There are quite few OBD-2 custom tuning software packages on the market, depending on what vehicle you have. Most of which can be found by a simple search on the internet.