The 1998 and newer GMT400 didn't have the chip in the key, the ignition lock cylinder and its housing is where the chip would be located.
Observe the "SECURITY" light, located in the upper right hand corner of the instrument panel/cluster. If the passlock/theft deterrent is disabling the injectors, the "SECURITY" light should be illuminated solid and or flashing right after the engine stalls(stalling abruptly/not sputtering out).
Here is a video which shows the location of the SECURITY light, etc etc.
https://www.youtube.com/watch?v=yDRwkEFLq-U
Looks frustrating, having a small part holding up expensive equipment. Have been down that road myself.
Some thoughts are, a excessively worn key might cause an issue, maybe try a spare/different key or have a dealer cut a new key from the VIN number and try that.
There are two fuses to check, one is the SECURITY fuse(10amp #21))located in the IP fuse panel, the other is the GAUGES fuse(10amp #4)also located in the IP fuse panel. Others have mentioned that those fuse numbers are easily misinterpreted at the IP fuse panel and I agree, maybe double check the position # of the fuses being inspected.
If there is a remote start installed on the vehicle, it most likely has a SECURITY bypass module or something similar, that should probably be inspected as well.
Here is a bit more info on how and why to reprogram the passlock/security.
PASSLOCK REPROGRAMMING AUTO LEARN
IMPORTANT: If a new vehicle/powertrain control module (VCM/PCM) is being installed for the first the manufacturing enable bit will be set and the auto learn procedure may not be necessary.
The following procedure allows for anyone to reprogram the EVO/PASSLOCK module learned data code with any tools, other than the scan tool, when any of the following parts are replaced:
The EVO/PASSLOCK module
The PASSLOCK sensor
The VCM/PCM
The EVO/PASSLOCK module will set the DTC B3031 in the learn mode when entering the reprogramming procedure.
IMPORTANT: Erase the PASSLOCK related Diagnostic Trouble Codes (DTCs) that are stored in the VCM/PCM.
The following is the Auto Learn Procedure:
1. Insure the ignition key is in the ON position.
2. Clear all EVO/PASSLOCK module and VCM/PCM DTCs.
3. Momentarily rotate the ignition key to the CRANK position (Do NOT start the vehicle), then release it to the RUN position (Do NOT key OFF in the process).
4. Wait 10 minutes . Observe the SECURITY indicator. Refer to the following list for the appropriate responses:
-If the PASSLOCK sensor was replaced the SECURITY indicator will flash for the 10 minutes duration.
-If the EVO/PASSLOCK module was replaced, the SECURITY indicator will flash for a few seconds and then remain ON for the remainder of the 10 minutes duration.
-If the VCM/PCM was replaced with a new programmed VCM/PCM and connected to the vehicle for the first time, the vehicle will start and this procedure may not be necessary.
-If the replacement VCM/PCM was connected to any vehicle at any other time, even momentarily, the SECURITY indicator will flash for a few seconds and then remain ON for the 10 minutes duration.
5. The SECURITY indicator will transition from flashing to ON briefly to OFF after 10 minutes if remaining in the ignition ON position.
6. Turn the ignition switch to the OFF position and wait for 10 seconds .
7. Repeat steps 3-6 two more times. The new security code is ready to be communicated among the PASSLOCK sensor, EVO/PASSLOCK module and VCM/PCM. The new password is learned on the next ignition lock cylinder cycle from OFF to CRANK to ON (start attempt).
In my case, with the key on, the security light remained illuminated and never extinguished. After proving the rest of the wiring and components good, I replaced the evo/passlock module(aka:theft deterrent module)and resolved my problem.
You might also want to search the forum for disabling passlock.
I guess there are a couple different ways of going about that.
Best of luck.