I've got one of these sitting in the garage, always loved the giant monster truck thing.
Had roughly the same issues as yourself. two things i found helped.
Engine heater! Turned over easier, fired sooner, idled alright.
25% nitro. It's a big old engine, and i remember mucking about with 16% and having no love at all. It fires better on 25!
Just my two penneths! Persist with it though, cos once they're roaring around the park, they look fantastic.
Don't corner, mind.