The 700R4 in my 89 developed some problems last night. As I went around a corner I heard a loud squeal for about a second and then the truck wouldn't move. It's like it was in neutral. I shifted it into 1st and it moved. Upshift to 2nd, it's still going, up shift to 3rd (or drive) and it still goes. If I put it directly into 3rd from park, it won't go. It's like it's in neutral. Haven't trid 4th (overdrive) yet Fluid level and condition appears fine. This transmission has been beefed with a heavy duty shift kit, Corvette sprag, extra band in the packs, etc. It's very stout as its behind a 383. But I'm at a loss on this one. I need ideas because this is my work truck.