Have used a miller dynasty and they are top shelf.i used one for 3 years at my last job and had zero problems,easy to setup,incredibly tight arc.i would buy the dynasty,but i am partial to miller welders so it is up to you

I weld everything with 2% thoriated,but i have used 2% ceriated a little.It works good but will erode faster!

I would be sure the lens is the right one for the torch you have.It may be letting air mix with your argon,but it almost sounds like a current flow,ground,or conductivity problem.I am not familier with the machine you have.If it has a water cooled torch or air cooled.This is what i would do-take off...