If you can borrow the tractor and chain, also get yourself a car wheel without the tire on it
A wheel off a car is the perfect size, nothing bigger or smaller.
1. Hook chain to tractor.
2. Wrap chain one complete turn around car wheel.
3. Save enough chain from wrapping around car wheel to wrap around T-post at the ground and hook the chain to itself.
3.1 Edited to say that the car wheel needs to be butt up against the t-post -- the rolling leverage is the trick to all this
4. You're ready to pull the t-post out.
5. Go easy on the gas pedal and I promise you the t-post will pull out of the ground and literally roll right over top of the car wheel with no damage to the T-post.
It's quicker and easier if there are two people. One to drive, and one to hook, but the "hooker" needs to back away from the chain just in case it does pop loose before the t-post is pulled out.
We have pulled a bunch of t-posts out that way --- works slicker n snot, so it does