I do not know its upper limit. It's a home-brewed thing so there has been no "scientific testing" done.
I am guess 600-800 lbs but that is pure speculation on my part. I did lift a snowmobile up into my truck, so I would rate it at "1 Sled"
I got everything from Tractor Supply and HF...
The "track holders" were 90 degrees off of what I needed, so I cut them and welded them to those short sections of angle iron (AKA old bed frame I had in my scrap pile...lol)
The winch is a Harbor Freight model, I think its a 1500 lbs (cant really remember that far back though)
The trolley holding the winch was/is 1 inch square tubingI had in the scrape pile. 3/16 wall If I recall. It was quite easy/fun to build.
Each "leg" of the trolley is independently adjustable so I could make sure it rode level. (although I am not sure thats a big deal or not)
I can post some closer photos when my truck is off the hoist later today/tomorrow if you'd like?
Aside: I love tractor supply, there is just so much cools sh!t there and there is something very appealing about buying hardware by the pound. I could spend hours there just walking around making things in my head.....