2005 to 2001 4.3 swap issues

[Caddyman53]

I have swapped a low mileage 4.3 from a 2005 Blazer ZR2 into my 2001 Blazer LT. I swapped the entire drive train (engine, transmission and transfer case) as one unit along with the harnesses. Everything fit and the only apparent difference was the exhaust heat pump isn't on the 2005 engine.
When I turn the ignition on, I get good fuel pressure and some of the gauges work. The fuel gauge and the oil pressure gauges don't read. When I attempt to start it, it will run briefly, and the fuel gauge will work in the start position. It dies when I release the ignition to run position.
I also can't get a link to my code reader and the MIL light doesn't show up at all.
I did a passkey reboot and the security light went out after the 4 stage process, this didn't help the issue though.
I have tried to find wiring diagrams online to compare the differences but am having no luck.
I would greatly appreciate any ideas as to where to steer my efforts.

Thanks,