You banged the cat and didn't hear any rattling so the cat probably isn't choking the engine.

First make sure this isn't just a bad MAP sensor. There's youtubes on how to test it but it's a pain and they only cost around $20 bucks.

You didn't say if the negative fuel trims were on one or both banks so I'll assume you have negative fuel trims on both banks.

You didn't say what percentage the computer was leaning the mixture on each bank either.

Hook up the scanner again. Go to Live Data mode.

I know you cleaned your MAF but observe the MAF data at idle. You have a 5.7L engine so the MAF should be reporting around 5.7g/s at idle. Make sure it isn't reporting much more than that or you'll run rich.

While you're in Live Data observe the ECT ( Engine Coolant Temperature) data. Make sure it's at a reasonable temp at start-up through warm up. If it's reporting a lower than actual ECT you'll run rich.

You have that CSFI Spider fuel injection system and if the MAF, MAP, and ECT are operating correctly then you need to dig a little deeper into what's happening with that Spider injector under the intake plenum.

But if you're lazy like me you don't want to remove the plenum if you don't have to.

You suspected a leaky injector(s) so you did the fuel pressure "bleed down" test. I assume you turned the key to ON to build fuel pressure and then turned the key to OFF and watched the fuel pressure gauge and from what you say the gauge only dropped a few PSI.

That confirms that you don't have an injector that's mechanically stuck open or a faulty pressure regulator.

It's time to see if there's a problem in the fuel injector circuit.

Specifically an electrical (ground signal) issue.

The injectors receive battery voltage through the ignition switch circuit (Key ON) and the computer "pulses" ground to each individual injector to control when and for how long each injector stays open. You have 8 ground signal wires to your injectors from 8 injector driver terminals on your ECU.

So there's 2 ways these ground circuits can fail.

A Break or "Open" in the wiring including a faulty injector driver in the ECU where the ground signal never reaches an injector(s) so the injector never opens. That ain't happening because you'd be running Lean, not Rich.

Or a short to ground in the wiring including inside the ECU causing an injector(s) to get constant ground and remain open all the times. That would cause a Rich condition.

It's time to do another leak down test. The first time you did KEY ON to build fuel pressure and then switched KEY OFF to watch for pressure decay.

This time you have to do KEY ON to build fuel pressure and remain KEY ON to keep providing battery voltage to the injectors.

You need to see if Ground is being provided to an injector(s) when it shouldn't be. (Either a short to ground in the wiring or a faulty ECU).

But you don't want your fuel pump to kick on during this test so after you build fuel pressure pull your fuel pump relay.

If you see the same fuel pressure decay that you saw in your previous KEY ON, KEY OFF test then it's not a short to ground or a faulty ECU.

If the fuel pressure decays faster, then an injector(s) is getting ground when it shouldn't. (wiring short to ground or faulty ECU)

You'll have to pull the plenum and determine which injector(s)'s ground wire is shorting out using a multimeter.

Your fuel injector ground controls are (probably) in the red 32 pin connector on your PCM (ECU). If you find that you're losing fuel pressure with the KEY ON/KEY ON test then you'll need to know which PCM (ECU) terminals are for each injector so you can test the wiring between the Injector connection and the PCM as well as the PCM's Ground Pulse to the injectors.

Buy a 1 year subscription to ALLDATE Diy for your 2000 Tahoe to see the PCM pinouts and the fuel injector wiring diagram

check the catalytic converter

Oh, and if you have an idle valve, make sure that's clean and working properly too.

Check the misfire topic in the FAQ in case I missed anything.