You are on the right track.
The 18X circuit is frequently a bad crank sensor which explains stalling when hot etc. When they replace the sensor, a CASE learn or crankshaft variation learn (same thing) is suggested. This lets the PCM learn the actual position of the crank and therefore it optimizes the control of the engine.
The smoke test, yes I'm familiar with this. The shop has a machine that pumps smoke into the engine, gas tank or whatever system is leaking and the smoke lets you find the leak quickly and easily. Probably the easiest way to find a vacuum/evap type leak.
00 Regal GS: All kinds of cool stuff.