Possessed Bonneville (update)

Recap: I have a 92 Bonneville SE (non-supercharged 3800 engine). Pretty good car, except that when it gets hot, it starts losing power. After the car has been driven a while, and while actually under load (not
power-braking, not revving in neutral), the tach won't go above 3000 rpm or so and bounces a few hundred RPM up and down.
"Hot" means the car has to be driven for an hour or so. The more time I spend on surface rods and in heavy traffic, the worse it gets. Heavy traffic especially makes the car malfunction.
When I'm experiencing the problem, the car lurches forward and backward, and won't stop this behavior until I let off the accelerator. The threshold RPM it does this at becomes increasingly lower the more I drive it, eventually stopping me from maintaining speed up hills and merging onto highways. The engine sounds like it's racing (but at variable speed) while it's in this mode, but very little net acceleration is delivered.
This car is possessed. It turns out that there was a severe exhaust restriction (the cat was plugged up). A mechanic finally got the car to exhibit the problem while he had a diagnostic computer hooked up to it and said the synchronizers (WTF?) were off, and concluded that the exhaust was restricted. He replaced the catalytic converter; the car's surging problem wasn't fixed, although it does have more power when it's cold (and thus running fine).
I've replaced: * Plug wires * Spark plugs * Air filter * Fuel filter * Catalytic converter(!) * Fuel pump relay
I had someone test the fuel pressure, finally. The results were a little odd: 30psi, increasing to 35 with the accelerator wide-open, but no higher. The needle also fluctuated slightly, maybe 5psi total, while the engine was on, which was worrisome. The specs state that I should have 40-47psi. Could this difference explain the problem?
One additional piece of information: the fuel pump relay is warm to the touch. Is this normal?
How should I proceed from here? It seems now that it's either an ignition problem or a fuel one, but I don't know which.
* Ignition control module could need replacement * Coil packs could be bad * Fuel pump could be weak * Could have a blockage in the fuel line(but why would the car only buck after an hour of driving?) * Dirty fuel filter (just replaced a few months ago)
The exhaust restriction is gone, but now I'm worried that whatever caused my catalytic converter to gunk up in the first place (fuel in the exhaust) will destroy this one too.
Thanks a lot!
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wrote:

$2.00 says it's the fuel pump.
Try this. The next time that it's acting up (i.e. hot & in traffic) pull into the nearest gas station & fill your fuel tank. If it is the fuel pump on it's last legs sometimes (not always) the cold fuel will bring it back under control for a bit.
I'll be interested to see what everyone else thinks.
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Full_Name wrote:

Hi...
How about the filter on the pick up tube in the tank?
Quick and dirty check for this might to just give the car a vigorous bouncing for a few seconds...
(Did it to myself a while back with overly generous use of injector cleaner and gasohol)
Ken
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Daniel Colascione wrote:

Without narrowing it down, it could be ign.module, crank sensor, or coil(s). Could also be cam sensor, MAV/MAF, IAC, TPS, ECU, or vac leak. (Along with an O2 problem.)
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