Intermittent No Start

[JessL]

My sister has a 99 Grand with the 4.7 that will just cut off and then no start intermittently. Have cleaned up all her codes, replaced the cam position sensor, crank position sensor, fixed some suspect looking grounds and gone end to end on connections to the PCM. There seems to be a security light occasionally. Any thoughts? About to order a new PCM.
Thanks for the help!

 

[duktrx]

Does that vintage of ignition immobilizer have the RFID in the head of the key; the one the size of a grain of rice, clear with the chip inside? Had a buddy who had a couple of late '90s vans, and had an intermittent issue with the security light in one of them. Turned out to be that little grain of rice, he could hit his key on one side and it would work then drop it and stop again.