Swapped a 1997 chevy tahoe engine for a 1999 suburban engine. Now wont start. getting gas & sparks. thoughts?

new crank sensor, new spark plug and wires, new spider assembly and fuel pressure regulator, new O2 sensors front and back, new timing chain, new distributor cap & rotor and much more.
Thanks.  I'm awaiting the delivery of the ECU.   Will also check the fuses.   will keep you posted.

I would suggest that if you can and have done that much work to the truck you should be able to "hotwire" it.  It is possible that some electronic device somewhere in the system is not doing what it should. Bypass all of the electronics and add a wire from the battery directly to the + side of the distributor. CAUTION...when you do this, you charge the coil and add electricity to the ignition system. Disconnect the rest of the wiring (temporarily) from the distributor so you don't "back charge" the electrical system. AS YOU KNOW, GASOLINE AND SOURCES OF IGNITION (sparks) DON"T MIX..be extremely careful.
With the distributor "HOT" turn the key to start the engine (you haven't disabled the starting system, just the "running" system) if everything else is up to snuff.....Gas entering the combustion chamber/distributor in correctly/timing gears matched up/COMPRESSION and a hot wire to the distributor...it should run.
To shut it off???  you need to disconnect the hot wire from the battery, turning the key will NOT shut it off....Remember...you HOTWIRED it...

If it runs, then you can reconnect the factory wiring and track down the culprit that is preventing it from running...