I have Z-Industries cal in my 95. The engine has run very well since I intstalled it in the late 90s. Back then, I tested it against three other cals, and the Z-Industries calibration made the most power at WOT, by a small margin.
Typically, on a cal for a stock or near stock engine with exhaust, Ron Zimmer will not add fuel and may actually lean it at WOT a bit. Spark tables will also not be changed much as the OE timing is pretty good. Zimmer does change KR strategy to take less spark out and bring it back in sooner. He lowers the fan-ons, disables skip shift. Additionally, some Z-Industries cals set the valet key default to "on" and have the idle speed up around 700 or so.
Generally, Z-Industries cals are pretty good for a stock, near stock engine and, even, engines which are fairly modified, however, Ron has not done a lot of recent development with the LT5.
I think the guy who currently has the best calibrations--mainly because he runs an on-going development program--is Marc Haibeck. He's one of the "tuners" who does have cals with altered spark strategy at part throttle.
