I have a customer with this problem, but its allot worst. The vehicle had no reverse one morning with just little warnings, a load bang that day she said and that was it, but she also wasn't listening for anything she said.
So i have seen this problem at the dealership i worked at as a mechanic but we had one tech that did all the tranny work, so i never got into them but did see it allot.
The sun shell gear teeth strip out and if your careful and dont drive it with no reverse, it should be less money for a rebuild. But some people do and when the metal pieces float around in the tranny it cause more damage, so dont drive it. If you do you will lose 2ND gear next, and it wont have 4Th either.
So as soon as you notice any issue with your truck, stop driving it on the spot, get the tranny overhaul, and make sure you use an aftermarket parts, the dealer parts are to soft of metal and you dont want to chance, try to tell your mechanic that this is common if he dont already know this.
The sad part of this problem is the part only cost $35.00 but $3500.00 later its fixed. The part in all the way in the middle of the tranny, so it has to be completely broken down to be fixed, so it will need a rebuilt kit, the sun gear and shell, and anything else the metal peaces damaged if any. The tranny I'm doing now didn't do any more damage and the lady drove it for days with no reverse, lucky!
So any question's about this problem, hit me up and I will try to help.
Any boat issues, i can help with that too and even will come and do the service if your in the state of Massachusetts.
Good luck