in my 1994 voyager with 3 liter engine and automatic transmission without overdrive, ive noticed when i change to reverse, it shudders. the van moves, but shakes. it also does the same in forward gear, but not as much. i am no mechanic or technician, but the oil is changed regularly and the shop that does it normally checks and adds transmission fluid. so it cant be a fluid issue. and theres been no repairs along the frame where engine installation points are. so, theres nothing loose there. what could be causing this? is this a transmission issue? is it clutch related? whats happening?