99 Tahoe Theftlock/passlock problems

I am having problems with my theftlock/passlock system on my 99 chev Tahoe. The truck starts and immediately stalls and the security light remains lit. It only seems to do it on warm (above 60 degrees) humid days. I had it in for service and they recomended having the ignition switch and module replaced. They wanted $1500 to complete the service. At this point they are just replacing components hoping that it will solve the problem. I am wondering if there are ways to trouble shoot this problem to make sure I am replacing the right components. Also a wiring diagram of this system would help. I bypassed the module on the ignition switch with a resistor and that seemed to work during the winter but now that it is getting warmer the problem has come back, making me think that it is something other than the ignition switch module.

Any help????

resistance will change some with temperature.i have installed several remote starters and bypassed security system i try to keep resistance at around 2-3 % of reading on dvom (volt meter)also ck for stored passkey codes ck conector at lower column