I am having a little problem, when I lock in to 4-Low its starts to move then slips like crazy then it will catch all of a sudden. It does not do this is 4-Hi. Do i just need to rebuild it ? It's in a 94 Chevy Suburban K1500 with a 4inch Rancho lift. 305/70/16 ProComp A/T, 4.56 gearswith a aurburn limited slip The tranny is a 4l60-e, TC is a NP241.