My 2004 ford mustang has not been run in over a year and it doesn't get any gas.Is this something to do with it's computer? It has very low miles.Is it the fuel pump or the fuel regulator?

Best to use a OBD2 code scanner and check for any stored codes.

may be late,bad fuel pump

Stay out of the Genie in a bottle isle

There has never been a manufactures factory service
manual or owners manual that require ANY additives to
any vehicle system

There not necessary & DO NOT WORK

The car is over 10 years old

Have the spark plugs been changed every 3 years
Have you replaced ALL the ignition coils around 6 to 8 year
or when they have misfired or failed
The front Oxygen Sensor get replaced on ALL vehicles at 100,000
miles
Have you been on a road test with a professional scan tool to look at data,have to do that a couple times a year
Is the EGR System working
Do you have any Vacuum leaks

Could go on all night

Just have to work on it several times a year

Have you checked for codes not just Generic
but Enhanced?

Use a bottle of yellow HEET dry gas to remove any moisture problem in the fuel.

Clean / replace air filter.

Top off ATF to MAX level.

check the air filter

dealer only computer glitch ,2005?? chances are its using encrypted software

A vehicle speed sensor that is starting to fail could cause this, or less than likely bad wiring or connections, or yes, a bad cluster could do this... But how exactly did she notice the speedometer was 10MPH fast?? There are no real accurate speedometers in vehicles (Don't get me wrong they shouldn't be off by 10MPH) but there is a 5 or so percent difference high or low in many vehicles even with stock powertrains. I've plugged in with a diagnostic scanner on many vehicles and the dash speedo shows 60MPH, but the electronic speed readout on the scanner reads as low as 55MPH or as high as 65MPH

Test alternator. Belt. Pully. These will all cause lack of power when your foot isn't on the gas.

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Sounds like crappy gas. The 289 may not like pump no-lead and the rattling sound you are hearing may be pinging / knocking.

replace plugs every 24000 miles or so(two years) buying good quality parts is another good idea. shop around, cheap parts are cheap for one reason. regular tune ups will help your car run and perform better. being easy with the gas pedal will help also