Well...bucking and slushing sounds aren't NORMAL...unless it's a Yugo...or a F*rd...
Was the truck warm? What was the outside temp? How long have you owned it?
Get the truck warmed up, in park,and on a level surface. Find your transmission dipstick, pull it out and take a look. Is the fluid at or near (but not over) the full mark? Is the fluid a clearish pink color? Nor brown or discolored? No "bits" of metal or grit/dirt in it? Does it smell burnt?
It's a start...
C.J.