Power loss problem with el falcon. NEED TO DO DONUTS SOON

Hey guys, just purchased an el falcon 4.0l auto. I use this car for donuts and burnouts ( got it for 100$ from a neighbour lol, and my mate has a big concrete slab at his farm so we use it there for donuts) problem is for the first 10-20 minutes on a cold start it makes enough Power for a standstill burnout, and can do donuts into second gear.
After it warms up though, will not do a burnout for the life of it, seems like it’s sluggish and loses a bit of power, although it still drives quite fine. But definitely a massive difference, even when full locking it and pushing the pedal to the floor when it’s warm it struggles to donut, then once I do manage to make it spin it’s just barely any power. Massive difference.
I was thinking gearbox but it is not slipping in the slightest, although first to second change does feel a little sluggish once it’s warm. Perfect when cold. Any idea what this may be? 185000kms. Got it from an old lady

Diff Bush ?