Snap On MW120 MIG Welder

.035 for both. It probably is old, because it's almost at the end of the spool. But would that cause it to wad all up and not feed properly?
Maybe. Just spitballing. So many variables. I’m assuming flux core. maybe some corrosion on the wire or swelling of the flux. Cranking on the feed tension is never a solution. When everything is running smoothly, you should be able to stop the wire with your hand at the tip and the rollers should just slip on the wire and feed again when you remove the obstruction (your hand).