Turns out that the idler arm is broken. My last extruder assembly had the same problem and I printed a replacement on my MakerBot Printer using PLA. The design is still loaded so I am printing another. I love Open-Source printers!
Are you using the same settings for the red as you are the other filaments? Individual spools can have different thermal properties due to dyes and such, so if you haven't already try printing the red at a higher temp than the others.