Anti theft light came on,stayed on for a few days then shut off,now the truck starts then stalls out after two seconds.Whats the problem??

fuel filter.

Anti-theft system has nothing to do with it . Battery cables , maybe , Park neutral safety switch possibly ! With anti-theft system problem you wouldn't a click or anything , that is if the anti-theft disables fuel or the starter . Plus the SECURITY light would be on if it were a anti-theft system problem . Your best bet , take it to a qualified repair shop that knows how to do starter circuit testing >
Starter Voltage Drop
How to voltage drop test starter motor circuit

And what's this identity anti theft system ? No such thing ! The vehicle has a content theft an vehicle theft deterrent system !
This system disables fuel not cranking of the engine. The VCM/PCM will not disable the fuel due to any BCM message for the remainder of the ignition cycle.
If the VCM/PCM does not receive the same password from the BCM as the last learned one, the vehicle will start and then stalls due to the Fuel Lockout.

Maybe it's the anti-theft system an not the remote start . Is the SECURITY light lit on the instrument cluster ? GM anti-theft systems will disable the fuel injectors if there is a problem .

Could possibly be the anti theft system. Check out this link. When the SECURITY fails, you should see a light on the dash that says security. A symptom of a failed anti theft is starting for 1-5 seconds and then stalling repeatedly. http://vatspasslockpasskeysecurityhelp.yolasite.com/

This could be an anti theft security issue. This happens all the time in GM's. The anti thefts are known to fail and cause the car to not start, stall while driving, or start for 1-5 seconds and then die. A good indication that the security is failing is if you see a light on the dash that says SECURITY or a picture of a car with a padlock thru the window. This link explains the problem, symptoms, and some DO IT YOURSELF solutions. http://vatspasslockpasskeysecurityhelp.yolasite.com/

it could be the passlock system ( anti theft system ). heres how to find out. all gm vehicles from 97-2005 contain an anti theft system called the passlock. on chevy malibu turn key on, let it stay on for 10 to 15 minutes. then turn ignition off, take out key from ignition, after 1 minute start the car. thats if its whats wrong. if this is your problem you can disable system for good ! go to www.tubesound.com/passlocksystem hope this helps,

your ignition switch could have carbon on the main contacts you should disassemble it clean it then reinstall it. the after market switches for that car are not very good. the switch is the problem causing the light to stay on. paslock is the reason your car will not run. the easiest why to fix it is- go on the net find a remote start companys one of them will have a genric diagram explaining what they have to do to get around paslock. with this diagram you can see the wire to cut and then insert the proper resister to resignal the paslock then remoce the resister reconnect the wire.

the big brain

This sounds like a bad key fob, when it starts and stalls after a few seconds means the anti theft system is on, the key may be bad, the computer may need to be scanned to get the codes, the codes will tell you if the key is bad, it sounds like you are locked out now after trying so many times it will lock you out, hope this helps, if you have a spare key try that one.

all dash lights keep coming on and either stay on or flash until you step on brake....also the dinger keeps dinging until you press on the brake.....we have had a tech work on it but have no idea whats going on.....HELP

sounds like petrol in the diesel ,