I have a 740 with truck maps installed on a micro SD card which was working great until about a week ago when it started getting sluggish, when first switched on all is well but after about 5 or 10 minutes the touch screen starts getting slow to react, if I take the card out and use the recommended nav on the internal memory all is well again. I have tried re-installing the Nav and maps on another card and it's just the same. I have also tried putting the truck nav on the internal memory and this slows the device down but when I re-install the correct nav all is well again. I can only assume the truck nav is a much heavier nav than the std one but I cannot understand why this has happened after a year of working perfectly. Anybody else had this problem with a 740?