I own a 2010 sport and the engine has 166k on it and am now having issues with my camshaft going bad and just generally my engine is seaming to go down bad,
so instead of buying a new engine and replacing the bad one I want a more efficient motor and was looking and found ford transit van motors for a pretty cheap 1000$ for only 11,000 miles on the motor.
but I have no idea how hard the installation will be my general budget for the upgrade is 4k and will replace it with my uncle who is a diesel mechanic.
but don't know if that's the most MPG I can get for a motor swap not to mention this will be my first swap so I have no idea how hard it will be I have done fab work experiences but I don't want to do something that is so challenging that I give up.

 

Welcome to the forum

2004 to 2011 Rangers are not good candidates because they are full digital, the dash and modules all communicate thru CAN Bus local network
So staying with current engine model will be best

If you change the engine model then you need to change Computer(PCM) which is a main part of the CAN Bus network
It CAN BE DONE, and has been done, just requires more work than you may want to do on your first swap

And if MPG is a main goal then ANY pickup truck is a poor choice, lol, a brick with 4 wheels that sits up high......................

That being said and since your uncle knows diesels look at Ranger TDI swaps
Google: Ford Ranger TDI swap

I think they still make the TDI adapter plates and "kits"

The VW TDIs can be quite fuel efficient, and there should be a lot of info on doing the swap, but cab electrical issues will be the bigger deal here