Here's a question, if you have the same Memcal, would the car run different. Let me explain, my original/stock Memcal is a 3506APYR - about a year ago I was told it was toast by my mechanic therefore I had a bone stock calibration of 3506APYR burned into a new Memcal/Prom which I purchased from TPIchips.com I found out that my original Memcal was not toast so now I have two 3506APYR Memcals/Proms. I gave my car a tune up about 3 months ago with the Memcal I had burned from TPIchips, the car ran fine but had a slight cranking issue that took me two to three cranks to start but otherwise it's all good. Just for giggles, I swapped Memcals and input my original stock Memcal and it seems to run differently, I notice it runs rich, I smell the exhaust and it's burns my eyes and idles slightly lower at about 500 rpm' vs. 750 rpms. Could it be possible that even though the chips are same (3506APYR), can it run differently??. Would it make a diiference if my car was tuned up with the TPIchip Memcal in the ECM and than swapped out with the original Memcal could that screw things up. Any input would be helpful

This could be due to the fact that the fuel corrections have been changed by the program in memory (after running for a while) and when you changed to the other Memcal that the settings are cleared.
It may run the same after some time for the corrections to take hold and be repeatable.
There could also be different revisions of the same program (factory changes) that have slightly different values.
The only way to know for sure would be to read the programs out and compare them.
The sequence code and date codes may indicate revision changes.

That took me a while to figure out. I'd burn a chip and the car would run like crap, so I'd go look thru the bin, burn one of the spare chips and it would run fine.....I had a chip that would say it got burned properly but it just didn't.