So if I understand your post the engine starts and runs after using starting fluid?
Or does it just fire up and then die with starting fluid?
If it's the first then your ECT sensor could be bad, this sensor tells the computer the engine is cold and needs extra fuel and advanced timing until it warms up, it is the "choke" for fuel injected engines.
It is easy to test this sensor with an OHM meter, so don't replace it, test it, because they rarely fail.
Your engine would also run "rough" until it warmed up, if this is not the case then it is not the ECT sensor.
The ECT sensor will be located near the t-stat housing, there will be two sensors that look similar, a 1 wire sensor for the dash board temp gauge and the 2 wire ECT sensor.
After cranking without starting fluid do you smell gas in the engine compartment?
Like engine is flooding.
When you first turn on the key do you hear the fuel pump run for a few seconds then shut off?
This is normal and if it does this have you tried turning the key on and off a few times before cranking, to prime the fuel system with more pressure.
If that works to start it then it means you have a leak in the fuel system that is loosing the fuel pressure when engine sits.
Reduced weight will give you better mileage, also reduced friction.
So smaller lighter and thinner tires would give better MPG.
But it would not be much of an improvement unless you do a lot of highway driving.
Rangers do not get great mileage, 14-18mpg with a 3.0l
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