Very interesting post. First off, I don't believe the ATS letter. ATS has PLENTY of off-road only products as well. For them to "tattle-tale" on the competition would only make the EPA look closer at them as well. I believe it is a hoax.
As for the emission testing on the computer controlled trucks.....The 1996 model year starting point is not accurate. Only Cali trucks (which had different PCM's that monitored GP's and other stuff that the 49 state programming did not do) are OBD-II compliant. ALL 97 and older PSD's are OBD-II EXEMPT...it is on the friggin valve cover. California has different OBD-II regulation in that it starts at a different GVWR, and many other differences from the FED regulation.
As for being able to tell if you had a chip at one time or another.....yes and no. The 94-97 PSD's will generate a code, BUT it can be cleared and after a few drive cycles there is no trace of any code. Trust me on this, I have done my research and I am an IDI and PSD owner. Besides, if you bought a truck used and the previous owner had a chip and removed it before you bought it, then how would you get a ticket for something you did not do with a part that isn't there anymore anyway! As much as I like the IDI's at least with my PSD I can switch my chip to a lower power setting and not blow any smoke when I don't want/need
to. Also, SEVERAL of the chips, programmers, etc. are CARB approved. You are not going to get a ticket for having a chip if it is a CARB approved product with and EO number. The problem with the internet and forums is that too many people think they are experts and take hear-say information and post it as fact. The state government has the same problem....several states were trying to OBD-II test 97 PSD's and they were ALL failing. The state didn't understand it's own testing procedure that clearly stated that 8501 GVWR and up only got tailpipe testing because they are not OBD-II compliant (and OBD-II port under the dash does not make it compliant...contrary to many)
Rant off,
Jerry