Hi Brian,
Well ... With some trepidation, here I go. Hopefully, anything stated in here is not offensive to any one ... It's not intended that way.
Tracy's Karate, to be exact, is Ed Parker Kenpo. The Tracy's originally studied under Ed Parker (as you may well know). After Ed Parker began to modify and change his art, the Tracy's kept what they already had, left the Parker fold, and there has been only some change/rearrangement since the early 70s. However, essentially, it is pretty much the same material as it was "way back when".
The basic forms, Short #1, Long #1, etc. up to Long #3 are pretty much the same in form... The interpretation of techniques within the kata are different.
Some of the EPAK techniques at the lowest level, yellow belt, are virtually the same except, again, the interpretation. Delayed Sword is a primary example. Same technique. In Tracy's it is a right punch defense, while in EPAK, it is a right collar level/shoulder grab.
Insofar as forms go, Long #4 is where major differences begin to show up, but again those are techniques. I surmise that this is because, as Ed Parker changed his system, the form became changed. Or, to keep slings and arrows off my head, mayhap the Tracy's changed it after they left. The reason I suspect that is incorrect is that nothing else was changed that drastically in Tracy's.
EPAK kept changing and modifying as Ed Parker developed and evolved. The Kenpo that the Tracy Brothers had did not go through those same evolutionary processes. EPAK scaled down the enormous amount of technique as it evolved, and became an analytical and defining method of study. Tracy's is a matter of rote repetition of already defined techniques, much like traditional systems of karate and kung fu.
Again, at the risk of suffering slings and arrows, there appears to be a niche for both perspectives in Kenpo Kulture.
Hope this helps some. It is really extremely brief, and doesn't have a lot of political, theoretical explanations or perceptions in it.
It is just simply a quick, topical overview of the differences.
Hopefully someone can add to or correct this thread as needed.
Dan