I have an 01 e150 with the 4.2 6cyl. The van is my work van and I have at least bare minimum 1500 pounds in it all the time some times touching 2000+. my question is, would swapping to 3.73s from 3.55s acutally hurt fuel economy since its so lugged down with weight? I want to believe it wouldnt hurt it and may even help it. Im getting about 13mpg average right now.

 

Changing the ratio to 3.73 will increase performance at the cost of fuel economy. 13mpg with a fully loaded E150 is going to be the best you can expect. Keeping the tires correctly inflated for the loads you are carrying will help a lot with your mileage.

 

my 5.8l had 3.73 from Ford. Now has 4:10 . It used to get 18mpg on the Freeway with a tail wind empty. now it gets 10mpg if lucky. But it will crawl up a tree .
Mine is a 4x4.

 

That is to be expected. Higher RPM means more gas is consumed.