Truck Slows down

[bassprokd]

1994 GMC K1500 (automatic). Gears and tires are stock sizes. When I'm traveling down the interstate and let off the gas my truck starts slowing down immediately. A lot more than friction would slow it down. It does it at all speeds but you can really feel it on the highway. It's messin with my gas mileage and I can't figure it out. When it does it, it almost sounds like it has an engine brake like my 4 wheeler does but I know it doesn't. Any ideas? Thanks!

[asilverblazer]

Seems like torque convertor can cause similar symptoms, like it isn't disengaging. Someone with more knowledge will probably chime in.