Slant won't drive over 25mph without cutting out

That is my next (should be first thing) to check. But I think it was mentioned. A good ignition with fresh parts! Worn out stuff will do what is going on. When the car is under load, driving and depressing the gas pedal making demands on the ignition system, poor &/or bad parts will show up as you described.

You’ll fix it. Keep at it. Freshen everything up one step at a time. You’ll get there.