I have a 1990 deville wont go over 35 mph

have exhaust back pressure tested. maybe the catalytic converter is restricted/ almost plugged. Also check your vacuum hoses for leaks.

If the fuel pump is original to the car & I would
doubt it,then that is the problem

Does the fuel pressure drop before it shuts off

I like to road test with the gauge taped to windshield
or tied to a wiper arm

You have to determine what your losing at the time it shuts off

I think you should have 55 to 60 # pressure

You could put that question into google for the answer

Fuel pressure regulator I guarantee you

several things could be causing your issue. start with the basics. when was last tune up? check fuel pressure, fuel filter cap rotor wires plugs make sure all are in good condition and correct pressure.

You've already eliminated the spark plug & wireset, distributor cap & rotor.
Sounds like your car needs a tune-up, specifically, the PCV (positive crankcase ventilation) valve, and/of the EGR (Exhaust Gas Recirculation) valve.

Components checked/replaced during a tune-up are:
air filter
motor oil
motor oil filter
breather filter
fuel filter(s)
fuel strainer
PCV valve
EGR valve
spark plugs
spark plug wires
ECM or distributor cap & rotor
cabin air filter
transmission oil filter
transmission oil
engine coolant
check all vacuum hoses and lines

Troubleshooting the no-start condition - from the 1990 Mitsu Mighty Max Repair Manual:

Priority Action Part Type -- Cause
1 Inspect Battery -- Battery Discharged or Faulty.
2 Inspect Battery Cable -- Corroded, Broken, Shorted or Poorly Connected Battery Cable.
3 Inspect Distributor Cap -- Distributor Cap Cracked or Burned.
3 Inspect Fuel Filter -- Clogged or Dirty Fuel Filter.
5 Inspect Ignition Coil -- Faulty Ignition Coil.
6 Inspect Wireset -- Worn, Damaged or Faulty Spark Plug Wire(s).
7 Inspect Spark Plug -- Incorrectly Gapped or Fouled Spark Plug(s).
8 Inspect Starter -- Starter Motor Faulty.
9 Inspect Fuel Pump -- Low Fuel Pressure.
10 Inspect Solenoid Switch -- Faulty Starter Solenoid Switch.
11 Inspect Fuel Pump Relay -- Faulty Fuel Pump Relay.
12 Inspect Fuel Injector Pressure Regulator -- Faulty Fuel Injector Pressure Regulator.
13 Inspect Ignition Switch -- Improperly Connected or Faulty Ignition Switch.
14 Inspect Starter Drive -- Faulty Starter Drive.
15 Inspect Fuel Injector -- Dirty or Worn Fuel Injectors.
16 Inspect Fuel Pump Strainer -- Clogged or Dirty Fuel Pump Strainerat.
17 Inspect Engine Control Computer -- Incorrect Operating Information Being Delivered and Sent From The EEC.
18 Inspect Fuel Tank -- Fuel Tank Empty.
19 Inspect Carburetor -- Carburetor Flooded or Faulty Choke.
20 Inspect Distributor -- Worn, Loose, or Incorrectly Installed Distributor.

If it revs up & doesn't go,the trans is slipping
& will have to be rebuilt

Not going over 35 with no trans issues would
be a bad exhaust converter (blocked) & or
a clogged gas filter

Tune-up is sort of a outdated term and never
is a cure for much ,unless you have ignition issues

Never have to replace any PCV Valves. Remove & clean
every 3 years

It should be either no Spark or no Fuel.
Possible causes: Out of gas, no oil pressure, faulty oil pressure switch, Bad fuel-pump, fuel-pump relay, needs tune-up, defective ignition control module, wrong air/fuel ratio, defective IAC valve or EGR valve.
Other causes: Wrong timing, bad compression, or clogged CAT.

Had a computer on my 1990 Cadillac Deville bad, after changing plugs, wires, cap, fuel injectors, egr valve, etc.

The computer was not firing an injector and i had a miss and rough running mostly at 35 mph on the roads. It bucked like a bull.in a rodeo.

A misfire on # 8 Cylinder which can be caused by poor fuel quality or metering, low compression, lack of spark or unmetered air entering the engine. 
There are other possible, less obvious causes as well. 
Fuel injectors, related wiring, sensors and computer issues
Running out of gas, or poor fuel quality
Evaporative emissions system (EVAP) concerns: fuel vapors leaking into engine
Incorrect Fuel Pressure
EGR system concerns: leaking EGR valve or restricted ports
Base engine concerns: low compression, valve train problems and timing issues
Ignition system concerns including, but not limited to:
Faulty spark plugs
Faulty coil or related wiriing
I would get the Dyno tuned and see what the computer is reading 35 and 45 MPH. or you could check with your local dodge dealer to see if there was a recall or update on the Computer if there was or is any issues. 
Good luck and hope this helps, Old School was so much easier.

have an exhaust shop check the converter, sounds like its stopped up