tranny woes

If you don't find it to be a shifter problem I'd guess it's a front clutch issue. Either the clutch plates are worn out, the clutch pack seals are leaking, or the reaction shaft seals are leaking. The front clutch is responsible for 3rd gear and reverse. Only way to check those parts is to disassemble it.

Have you pulled the dipstick out and smelled the fluid? If so did it smell burned and/or look brown?