My hope is your estimated weight is off by a lot. If he's 125 pounds at 4 months old he's in serious trouble. Especially at those temps. Maybe post a couple pics of him. That can help determine a plan.

First thing I'd do is wean him off the replacer. He's plenty old enough if he's 4 months old. At this point it's not doing him any benefit if his weight is as you've said.
Have you seen him eat the hay and corn? What about water consumption?
Chopped corn isn't enough for a bottle baby. He needs a good quality starter and he needed it in front of him from the start. They need extra nutrients to keep up. If you have replacer left you can sprinkle it onto the starter (dry) for a bit of extra nutrients and to help him eat it starting off.
Fescue/ clover mix hay won't cut it either in this situation. He needs a fine stem alfalfa at this point. Just don't push the alfalfa AND starter all in the same day. Offer the alfalfa along with your fescue/clover (mixed) and a small amount of the starter twice a day. You'll overload his gut if you throw to much nutrition/calories at him at once.
Also if he were here I'd give him some probiotics. Especially if he's having a rough go with the temps etc.
You said you almost lost him already. I'm glad you didn't.

Good job keeping him going!
What is his housing situation?
I'm rooting for you both!

Good luck!