1992 Oldsmobile 98 Oldsmobile starting problem

My 1992 Olds 98 Regency with a 3.8 V6/electronic fuel injection is hard starting. The car has high mileage, but I suspect it received a new engine sometime (I bought it used).
The car was at first hard starting hot, but now it can be so hot or cold. I have done the following, to no avail:

1. Cleaned plugs (plugs were in good condition)--plugs and wires are fairly new.
2. Checked ignition module-good spark.
3. Checked fuel pressure regulator-got flow of fuel from schraeder valve after ignition on (not cranking) for a few seconds.
4. Installed new crank position sensor.
5. Good battery connections.

Can you help me?

Thanks,
Mike

updated by Admin 5/26/09
I have checked the coils for spark by removing the wires and observing.
All terminals display strong spark arcing. Seems OK. One thing I did not notice until yesterday: one of the injectors makes an intermittent, brief hissing sound. If you think this indicates clogging, can I remove the injector, spray the tip with carb cleaner, and get better results? I've tried injector cleaner in the fuel.

updated 6-16-09
Sorry for the delay in responding. Had to get a fuel pressure tester.
My '92 Olds fuel pressure range should be 40-43 psi. When switching on
ignition only, and not starting the engine, pressure goes to 45 lbs,
and then drops to 0 when the fuel pump stops running, with the ignition
still on. There is a leak in the tester, which causes gasoline to drip
out the guage hose, but it does not seem to be too serious. I checked
the fuel modulator for vacuum tightness, and it seems OK. When running
the engine, pressure reads a constant 37 psi. I ran fuel pressure tests
with the gas tank pressurized and depressurized (gas cap on and off). I
also checked each injector with a mechanic's stethoscope, and got
distinct tapping noise from each. As mentioned earlier, the ignition
module gives strong arcing sparks between each pole, cold or hot
engine. Wires and plugs in good condition. I also put fuel injector
cleaner in the gas. Starting problem persists.

Thanks for sticking with me,
Mike

updated 6/27/09
Thanks for the help. One thing I neglected to mention was a strong smell of fuel after cranking the engine too much to get my '92 Olds started when hot. Any reactions to this?
Thanks again,
Mike