Art Good

These Trucks can be a real problem. I was wondering if you could give me some advice. I'm working on a 2003 Silverado 2500HD 6.0l. It was driving down the road and got a reduced power message then shut off. When checking it out we had no communication with the computer. So I replaced it programmed with the proper data and VIN#. It would not re-learn the key. I did what I should not have done and shorted the two wires on the passlock. It learned and ran fine for two days and then the same thing happened. Difference now is that the computer communicates fine. I reconnected the passlock wires but the security light will not go out. Every time I try to start it the starter kicks in then immediately kicks back out and so does the starter relay. When testing the circuits the thing started, 20 times. The next morning I went out and same thing starter just kicked in and out. An hour later when I went to check voltages again it started, again I started it several times. I'm afraid to take it anywhere because it may shut off or just not start again. Could this now be a passlock problem? Usually if its a passkey problem it will still start for 3 seconds and not just kick the starter back out like this truck is doing. I'm not getting any codes but don't have a device that will check the BCM. Any advice would be appreciated.