Searching for info on where to buy a rebuilt automatic transmission for a 2008 Ford Ranger 4x4 with the 4.0 litre motor.
USA or Canada. Any help would be greatly appreciated.
It presently 'free wheels' in overdrive and third seems to be very weak.

 

I'm not on the Welcoming Commitee, but WELCOME to the Forum!
How many miles on your truck and on its transmission?
How long have you owned the truck and has the transmission ever been changed?

What does "free wheels in overdrive" mean? Does it feel disconnected from the engine whilst in OD?
And what does "third seems to be very weak", mean exactly?

Heave you looked at and smelled the fluid?
You'd be surprised how often a pan drop with filter change improves operation; even though only ~1/2 the fluid is refreshed.
Also, this simple maintenance procedure is not expensive.
Get a 6-pack of MerconV and a filter which includes a pan gasket.

Having your unit rebuilt by a competent shop is likely the way to go, if a rebuild is needed.
Given the horror stories about 'mass market rebuilds' on the internet, a Ford dealership sourcing rebuilds from a familiar company, might present the best mix of quality and price.
You're in Alberta. Are you isolated? Do you have people to ask?
You've a bit of research ahead of you.
Good luck.

edit: I've read here that there are two kinds of rebuilds, a 'soft -just friction pieces' and 'hard-or complete'.
If you have yours done or do a swap, the word is to get the completely rebuilt one.
The soft item rebuilds don't have the same longevity.