dcnbre

I have a 1998 chevy k1500 with a 5.7 vortex, when driving the truck has a hiccup , it dont matter of I'm pulling or just normal driving , no ck eng light comes on. Just had the transmission rebuilt , it has 143662 miles. I just pulled the rear diff cover and noticed that the oil was black! For I just replaced the diff oil a year ago , could my hiccup be the rear diff ? I have 3.73 w/ limited slip