When I do a burnout it's always my left tire that spins but I noticed that sometines it switches is this normal for a truck without posi

 

100% normal. In an open diff (no locker, limited-slip, or posi) the engine sends power to the rear end and spins the wheel with the least resistance, right or left. This is good for the average driver, but if traction is your goal, an open diff is not the answer.