My truck sometimes won't go in reverse. I either have to let the car warm up for a couple of minutes or put it in drive and then put it in reverse. My transmission is fairly new, only 3 years. Can anyone tell me what I should do?

Take it back to the shop that rebuilt it, if possible? Losing reverse is a classic sign that the trans is about to die.

Thanks. I took it in and they are doing an internal inspection today.