Sx-15 not good at larger stuff, makes evil noises..

[Truckntran 0]

Hi everyone, glad to find this place.. I do signs as a fill in between other work, and have a Roland Stika  SX-15 I bought used, using it with DR Stika on Vista.

If I try to make a decal that is any larger than say 10 inches in length, it occasionally "burps" and relocates the lettering anywhere from half an inch to an inch away from its location.. Sometimes this is accompanied by a rude "Stripped gear" sound, other times no audio indication, I just find the error when weeding.

If I try to cut out an oval , say two feet by ten inches, with words inside it, especially if I use a "star shaped " oval, it will do this nine times out of ten..

I have paint masking I cut last night (actually just odd vinyl) where it was simply a large 10 inch letter with a border.. In 39 inches of cut area, the border tracked off by about 1/4 inch up to a half.

I have tried not cutting off a roll ( I have a nice roller stand for the roll) to lessen the load on the drive rollers, and I cleaned the roller wheels and the drive shaft (I couldn't believe they use adhesive perforated foil for traction on the driving shaft..)  and so far have only been able to limp my way thru the larger decals.. If this wasn't a paint mask job it would look like poop. I also have tried cleaning and resetting the depth on the blade, and even a different blade.. 

Any Suggestions?  (I know , new cutter...but that is in the works after I do enough signs to buy a Camm or graphtec or...?? and I'm spoiled by DR Stika's ease of use..)

Thanks in advance for any help...!!