new here having trans problems

Joined up to try to find answers as to why my tranny quit, but no luck finding any post related to my problem. Not sure which forum to post it in it's a 96 Ram 2500 cummins. I bought the truck with a bad TPS, pevious owner had wired in a pot under the dash to make it work. I put a TPS on it, took it for a short 3 mile drive half way I took it easy and everything seemed perfect, shift points good and smooth. I then dropped to 45 mph kicked it to test for kick down and it dropped to 3rd perfectly, shifted to overdrive at about 65 then the lock up kicked in at about 70. then I lost all gears no movement in any gear. Park does still work. Truck basically stock as far as I know, bought it from an escort service, so doubt any mods done to it, AFC still has tamper proof bolts. Checked fluid after sitting overnight and it was way above full, cranked it up and put it in neutral, let it run for a bit then checked fluid and it was just under the full mark but above the add mark, so pump seems to be pumping. not sure where to go from here any input or a link to any help would be very much appreciated.



Thanks for your time