I am using a 25' 12ga extension on the Hobart 140 and it welds good. Sometimes it's just a tad slow starting but the ground clamp is not very good either so if I fixed that it would start quicker.
So many things could cause current to drop and a rod to stick so I can't diagnose it over the forum, it could be everything from the wall plug to the electrode is good but there is aluminum wire inside the wall. Who knows.