13 speed overdrive slips out, pops out

Sounds like you have a mechanical problem in the rear section.

 

Does the problem happen with your hand on or off the shifter when coasting? Or both?

 

that could be dangerous.....does it happen if you leave it in 8 low and take your foot off or is it only 8 high. have you tried the high side of any other gears? (7 high going slower with foot off down hill)

 

When it slips out can u slide it back in? Or do u have to make a shift? If it slips out in the tranny and does not slip back in when u gently pull down on the shifter it's time to get that tranny out ASAP. Because the reman that u bought was not a good one and will blow right the *#%^ apart at 70 mph.

 

I've heard of this before, the last truck I drove was doing that. The gears are angle cut to lock in under load, when you are on the throttle. They have some kind of clutch like springs in there to hold the gears together when you let off. If the springs are worn out, it will pop out of gear like that. I think what you need to fix it is called a helix kit. I dunno how much that costs or how much work is involved though.