Need help with the 3.7L

Mmmmm, OK, did you run the gas from the jug and actually drive (brave or foolish man LOL!), or just run the gas from the jug in the driveway? The flow rate while driving is a lot more.

Can you describe 'falling on it's face' a bit better? Does just drop out instantly or does it falter and sputter?

And the gas being clean does not mean that the tank is not full of crud that is being sucked into the system. It'll keep plaguing you unless you get past that.

Sure, the carb could be it. But the initial symptoms don't seem to indicate that since it sounds like you can drive around at 40-45 mph OK. If you are driving at 30-35 mph, can you accelerate just fine up to 45-50 mph?

Since it could be a number of things, then a process of elimination is needed (like you sound like you are doing). Do you have acccess to a fuel pressure gauge? (And a voltmeter just in case?)