Crank, No Start

I have had a problem with my car not starting for several months now. It is a 1998 Chevy Monte Carlo, Z34 3.8L 3800seriesII. It has 111,000 miles. It would intermittently "crank, no start." Doesn't matter if ignition is toggled (hear buzzing of new fuel pump), pushing accel. Pedal down also no help. Ive only tried starting it for about 5-10 secs. Didn't wanna do damage.
So I had the fuel pump replaced (check engine light signaled low fuel press.). Didn't work, so I also had MAP sensor replaced (faulty readings) along with ignition module because I had heard that part fails frequently in models this old. On the list of things replaced/checked: fuel pump, gas filters, starter replaced (2x), crankshaft position sensor checked ok, injector relays ok, MAP sensor replaced new, gas cap (fuel pressure).
When it does happen, usually I dont think the weather has any affect (although the most recent time was after long rain). It has happened in cold and warm weather. It has happened shortly after running engine. It went a solid month without happening, then again. Most important, when it does happen, it will usually start up right away without hesitation if I let the car sit an hour or so.
Most recent was map sensor and ig. Module repl. Which seemed to cure it, until it happened again. (Now, Check Eng. Light comes on sometimes a few seconds after starting up, but will not come on the next time car is started).
Thanks, and sorry for the long post, but there are a lot of things to explain. Please help with some advice!