I replaced my impeller earlier this year and what a pain it was to get out. I bought a can of silicon spray, similar to WD-40 and sprayed a bunch all around the impeller then let it sit for a bit. Came back sprayed some more then it slowly worked itself out. Took a lot of effort and getting any leverage is not easy, I think my forearm was bruised for at least a week. Sprayed the new one with the same silicon and it slide right in.

The overheating issue may be due to the impeller, not sure though. Is the oil good?