Craftsman T1000 runs weak after about 5-10 minutes

I saw another very similar post with the same mower and situation. Mine will start and run fine, after about 7 minutes seems to lose power, RPMs are reduced. Especially under a load. It seems like it would stall soon, but I've been putting it back in the garage while it could under it's own power and finishing with another mower. The next day, same pattern. I've cleaned the air filter, replaced the fuel filter, spark plug and ignition coil - same thing. It uses some oil, sometimes when first starting I'll briefly see some white smoke. Also tried running with the gas cap loose.

I've heard it could be a bad head gasket. I don't see any signs of oil leaking. I sort of cleaned the carburetor, meaning sprayed cleaner with the choke open. I've heard these Zongshen engines aren't the best, I bought the tractor from my late neighbor's estate in 2019. He bought it in 2016, I had mowed the lawn a few times with it since then. It was always ran fine until the last fall and got progressively worse with the symptoms. It did get very low on oil once, and about a month ago I found a huge mouse next under the shroud. Maybe the damage is done due to overheating and running low on oil?