1998 Volkswagen Jetta Timing Belt OR Transmission

Whats going on.I have an automatic volks, jetta. 1998.5 version. When im in reverse it takes a second or two to kick into gear then it works perfect. Sometimes but not often, when first starting the car. First gear slips.

ive been told twice that it could be a loose or weak timing belt (if that goes, my whole engines done). Ive been told my transmissions going. And a fluid change will only make it worse. Though ive also been told if I get a new tranny fluid filter with a change my car should run perfect.

im not sure what it could be for sure and would like some help.. Thanks in advance.