HouseCallAuto 4/21/2013I have never seen anything but a new transmission solve this. In my 36 years fixing vehicles of all kinds.
naterenfo1 4/22/2013Time for a rebuild bud! Your clutches in your transmission are worn out. The reason why it went into gear before, was because the clutch material that had worn off of the clutches was suspended in the transmission fluid, and would at least allow your truck to move. Now that you have put new fluid in, and put a new filter in, there is no clutch material in the fluid and the clutches can't do anything but slip past each other. Tow your truck to the nearest transmission shop and have them take a look. I can just about guarantee this is the case. a rebuild for a 4x4 ram around MN is looking at about $1,500-$2200 with new torque converter, removal and installation at a small town shop. Dealership would probably be double that.
My experience comes from working at a small transmission shop in Alexandria, MN. Best of luck to you, and I hope your wallet doesn't take too big of a ding!
-If the place you have your transmission rebuilt at doesn't offer to put a new torque converter in, find a different shop. Never re-use a torque converter.
-Make sure the transmission lines get flushed
-Have the shop change your transfer case fluid while they have the transmission out. Good preventative maintenance! and I can't remember off hand if the transfer case shares the same transmission fluid or not.