I put an aftermarket ign. module in my 1993 Blazer which was a 5.7 TBI. After that, the truck would stall three or so seconds after I came to a stop while in 'drive' at lights, etc. If I put it in neutral, it didn't happen. I wound up getting pissed and changed the whole distributor which solved the problem. I got a new complete one from a dealer, lol. For some reason it wasn't much more than when I found it online, it was a GMPP one.
A year or so later I threw the old dist. on CL as a parts unit or whatever and noticed that the AZ aftermarket module had a huge bubble in the shiny part on top. Apparently it was junk out of the box (I did follow procedure installing it with the heat sink grease and stuff). Looked online on forums and such and the common consensus was that many of the aftermarket modules were garbage for the TBI applications (same with aftermarket 02 sensors, etc.).