Tuners leave signatures???

I've been wondering if these tune-up artists that some of you have tune your rigs leave any kind of I.D. visable on the ECM?
I bought a used 03 Z71, 5.3/auto trans, ex-cab that I fell in love with on the first test drive. This thing ran like a raped-ape!!! Got 17mpg around town, would chirp the 265/75R/16's going into second gear and pulled 8000 pounds worth of horse trailer like it was fun. This truck had stock exhaust, and the only thing I found that had been done was that K&N air intake.
Was it tuned??????? Of course by looking at the ECM, I couldn't tell. I've driven several other trucks since I got that one and none compare.
I finally broke down and traded it this week. I had to go bigger because of the towing. Got an 04 2500 with the 6.0, it doesn't run anything like that 5.3. Missin it already.

It sure sounds like it was tuned. But sometimes there are a few trucks that just get tuned "special" from the factory. Theres a 2000 GMC here that runs like hell and gets 25+ mpg all day long from the factory. I guess it was just tuned better than the rest that day.

I'm getting all the gear and programing together to start chip tunning myself, I got the idea from, thirdgen.org.
I know they can do some pretty killer stuff with just reworking the chip on camaro's, firebirds and vett's, I plan on keeping my deal a GM thing only, no imports.
You can change shift points, timing curve, injector pulse width, speed govener, etc.
I can't wait to see what I will be able to make my truck do with all this

I use either the PROM/Mask I.D. byte to encode the month/year of the programs I've written to a PROM, plus the BCC label on the DIP or case itself. Some people probably just burn a program and forget it, but it's nice to be able to read a binary and know that it isn't a factory or stock tune.

On the subject of programmers . Yesterday I read on jetchip.com that their plug up programmer can only be used on one vehicle . It copies the VIN into memory and will not except another . Rob