Michael Luce

I have a 95 ZJ Grand Cherokee with the 4.0 and 42RE transmission. The problem I have is when Im driving and get to I think 40mph whenever O/D kicks in it will start grinding and also kind of sound like a belt squeal. Now when I hear it I hit the O/D off button and it goes away and drives fine. It does lurch when idling around for say around a parking lot, and jerks from 1st to 2nd not bad but you notice it. My backyard mechanic had fixed this issue one time before, with a part he had in his yard (used) and it fixed it but with the amount of work he does he forgot which one it was. Im thinking like (VSS) vehicle speed sensor which is on the tail shaft but from what I understand there another speed sensor of some type on the driver side of the tranny. If someone could explain these sensors to me and which on is what It be appreciated. I do know the VSS can cause draibility and transmission issues but Im not going to waste my money away just throwing parts on.