ECU Trouble Shooting

Been having a lot of weird issues with the truck. Today's latest and greatest:

Each weekend I start it and run it around the neighborhood and allow it to warm up to normal temps. Last week ran ok except the AFR's would never normalize; more on this later.

Today I went to start and battery was dying. When I hooked it up to jump start, I heard some clicking in the Throttle Body, like a relay or something.

I started it up and let it run but when I turned it off, and removed the key, truck was still running. I couldn't get it to shut off. I pulled the EFI fuse to shut off the motor but truck was still energized and dash still lit up.

I disconnected the battery and the ECU reconnected everything and it started up and would shut down just fine, but it idled like hell (AFR's in the 19's-20's) and threw a P0100 code.

I replaced the MAF and it threw P0100 and P0110 code. I turned it off and removed the AEM FIC piggy back controller and it started up and the code never came back but it still ran like shit.

I reconnected the AEM FIC and code still didn't come back and it still ran like shit (AFR's still in the 19's-20's)

I took it for a drive and all of a sudden, AFR's normalized and the truck ran great. Took it on the highway and back, no issues. Turned it off let it sit and started it back up and now AFR's are fluctuating between 12 and 18 (been doing this a while). If I start to drive it again, usually when it shifts into 2nd gear, AFR's normalize.

I have no Idea where to begin. Bad ECU? Bad fuel pump? Bad Fuel Pressure Regulator? Vac/Exhaust leak?

 

Anyone know if I can use an 03-04 ECU (4x4, AT, PN 89666-04040)?

Current ECU: 01-02 4x4, AT, (PN 8966-04820/04821).

Im running the 04821 ECU.