Trans fluid $$$???

Yes you can run hydraulic oil in a transmission. Race guys have been doing it for years. It will tighten the converter up about 2-300rpm and it WILL shift harder. You have to make sure you buy the stuff for wet brakes hydrostatics etc. John Deere hy-gard is good. They make 2 different ones. A normal viscosity and low viscosity. Both work great. Hy-Guard is actually better than trans fluid as it can get to like 400 deg before it burns. And it doesn’t foam.