I have a 1994 B250 conversion van , it has 135,000 miles on it, 318 with the A518 transmission. I use it mostly to haul my motorcycles around. I also try to drive it to work a few times a month at least if nothing else. We've been using it the last couple weeks a little more since my Durango is down for repairs. One thing I noticed in the last few months is that the shift to third seemed to take a little longer than usual. (not sure if that has anything at all to do with what happened last night) We had a 15 mile run up a highway that had a 70 mph speed limit, and it was cruising just fine. We got off the highway and about 4 miles later on a twisty road, the van slowed down and seemed to lose power, and like the brakes came on the way it slowed.... I hit the gas pedal and it revved but we were not going anywhere....I thought the transmission failed by the way it sounded and acted... I pulled off to the side of the road. After we gathered our wits, I managed to pull off and up the hill, no slipping or anything....BUT,,,as soon as I made it to about 34 mph, the van started slowing abruptly again like it was going to lock up...I flipped it up into neutral and coasted to the side again. I thought I would limp it home but every time I got much above 30 the same thing kept happening. I cant remember why I tried it, but I reached over and hit the overdrive defeat switch. No more problems, although of course overdrive was disabled. We made it the rest of the 25 miles home without an issue. I drove it today with the overdrive disabled and worked just fine....hit it hard, no slipping no complaining... I re-engaged the OD and carefully took it up and at about 35 mph it started it's slow down again...no grinding, no sound, just a super drag like the brakes were on. Obviously it has to do with the OD....did I blow it out? Im thinking everytime the OD tries to come on its jamming up or something. 35 seems a little slow for the OD to want to kick in so that also seems weird, but again with the OD defeated it never happens. If I am correct the OD on the A518 is hydraulically controlled, no electronic components yet in 1994. So whats it sound like? If OD is shot can that be serviced short of dropping the transmission? Even if I have to drop the transmission I wonder if I can repair the OD.... Thanks in advance for any input!!