i have a 96 blazer with the 4.3 which has decided it doesnt want to shift from 1st to 2nd. the only way i can get it to shift is to run the rpms up to 4000 then back off and it will shift, but hard. i dont know anything about transmissions and it just started doing it and i havent had time to take it somewhere. does it just need serviced or a new filter or what? someone tell me something