Well, 2002 Silverado with 5.3 z71 package. Put it in reverse to park the cattle trailer, it shows that its in reverse. Give it a little gas, truck does not move at all, no rocking no clunking no nothing, it just raises the RPM. Has happened a few times when I'm just going in reverse, i get the RPM to around 1,500 and i stop, let it idle. then release the brake and give it gas again, it goes to 1,200 and then catches, and spins the tires(gravel and grass and stone surface). This is very concerning, there's been alot of things wrong with my truck thus far(january), and this is only adding to my bill. Also, when i turned my truck on today, i had in the display thing(can't remember what its called, but it shows your "Change Engine Oil" in orange) Well as i was saying, it said "Service 4WD" or "Service 4x4" for less then two seconds. Then it went away. Drove it away for a block or two. Started it back up. And it didn't say anything. I'm needing to go get my codes read very badly i guess. There's a bunch of other problems with my truck too, some ticking when i start my truck and drive it for a bit, until i romp on the gas. Then it's gone, just did a full oil change. Did it before oil change, and still after.