asko 7005 dryer belt/motor ?

replaced the belt in my asko 7005 dryer withe the appropriate belt, and there seems to be a bit of slack in the belt, as it will spin with a very light load (i talking, 2 shirts and a pair of jeans!!), but when a full load (not an elephant size or anything) is attempted it doesn't spin!! I spun it by hand and when i stoped it from spinning, the belt would slap/or vibrate against the drum...ie: feeling like there might be to much slack or lack of tension. Not sure if there is somthing wrong with the motor (maybe lack of torque for some reason). The spring looked fine as well.... Not sure if i'm missing somthing completly ovious or there is some bigger issue... Please help!!!!! Thank you for your time..