The answer to that is really more of an opinion than a fact. It seems that different cars respond differently to different chips. Get the difference? It seems as though Jim Testa's name comes up when there is a tip-in stumble problem with certain cars. There have been a few guys who had this problem with various chips until they got one from Jim. Most of the chip makers in the TR community seem to have these cars pretty much dialed in when it comes to burning chips though. Most of the time, it's just a matter of a little tweaking here & there. Lance gave a good explanation of it in a post above. Well, below now. HTH
Have you called Casper's about a chip? John sells them with anti-theft thumb wheel. Also single chips. I use his and it runs clean and no stumble off idle..... alan http://www.casperselectronics.com/