First off, new to welding, so if something seems obvious don't hesitate to mention it!

Trying to fill in 5/16 holes drilled in 1/4 aluminum. I'm welding with an Eastwood mig 135 with a spool gun and 100% argon.

Been working on this project for about 2 weeks and had things pretty well tuned in, or so I though. After welding about 2 hours today, everything starting going down the toilet. The wire started burning off. The gun acts like it's too hot, but I didn't adjust any of the settings. I let everything cool down for about 20 minutes, but when I resumed, same deal, wire melting back to the tip as soon as I start my arc. I reluctantly lower my voltage and increased my wire speed, despite the fact this has worked fine for several days. Doesn't seem to get any better. The only thing that i'm wondering about is my argon tank is getting low. Now, its not out, just down. At this point, i'm grasping at straws. Any thoughts?