Avic N1 and GMC Security Issues ?

I put in a Pioneer Avic-N1 into my 1998 GMC Serria about a month ago and had no issues for about a week after the install was done, since then about once a week my Security light comes on the dash and after a few more off and on's with the ignition the vehicle wont start.

It started by going into the shop and the vehicle not starting, it would turn over and only stay running for about 3 seconds. To make a long story short once the Avic was un-plugged the truck fired right up. Another week or so went by and same thing happend, truck wont start so un-plugged the head unit and the truck would start. My dad own's a automotive shop and we used the scanner and it come up with the code P1626(Anti theft Device) we thought it may have been the ignition cylinder getting worn out so we replace it and coded it to the vehicle.

Truck ran fine for a day or so and same thing is happening again, sad new is the factory head unit is back in and it causing the same issues. Has anyone come across this happening to them or anyone they know? I have googled the topic and found a crap load of info but no one has really said what the cause was.

I did the install on the unit myself  and have knowledge as I was a installer for 6 years, all that was installed was a factory wire harnes and mounting kit.

Thanks,

Jr

It is dissabling the Fuel, it runs for the 3 seconds and then shuts the injectors down. VSS and rearview are not hooked up.

I had the column apart today and all wires look just like new, I checked voltage at the top near the cylinder at the 3 wires for passlock and the voltage was the same at the top as it was at the main plug under the dash near the steering column.

The security light will not come one when it wont start when the key is first turned to the run position, when it does start the security light turns on for 5-7 seconds then off it goes and it starts like normal.