Ok, I might have had my years screwed up here, but our truck is a 97, 5.7 liter, and has that stoopid spyder setup that I don't like. Yours is a 2000, and I guess that the 2000's had a 5.3L? I guess I thought they switched in 2002 I've been wrong before, I know what it looks like. If you have a 5.7, it is probably (I'd lay the lumber on it) the pump, if it is the 5.3, it might not be. I was told the same thing, fuel pressure regulator leaking, but I diagnosed that to be functional. I just hooked up my fuel pressure gauge to the schrader valve and clicked the key. I wasn't looking for a specific number here, but if it held pressure, the regulator would not be leaking. So I was sure that the regulator was good. I was pretty happy about that because that regulator (on our truck) is part of the stoopid spyder assembly which has to be replaced as a unit at a bargain basement price of $400, probably closer to a "G" at the dealer. I did all the same stuff you did, new battery, new fuel filter, and I chased and cleaned all the grounds it wasn't until I came across the specs for fuel pressure that I realized what the problem was. Then I did the same check and sure enough like 58-59 PSI at the schrader valve which is not going to start the truck (again our truck). It made sense after I sat down and thought about it, little lady ran out of gas, I remember going to fill it up with a can as it sat on the highway. Hard starts after that and then wouldn't start at all.
I'm not trying to be a Jerk about GM, I just added commentary for color, so appologies if I offended anyone who is employed by or a fan of GM. I like the 'burban, it is very useful I just don't like some things about it.
Good luck on getting to the bottom of this.