You likely have a broken forward apply band and this is a somewhat common problem once the mileage starts getting up there. When the lug on the forward band breaks it cant hold so it will just rev in D or 3 range but in manual 2 and 1 there is another band that applies for extra holding power and engine braking so it will get you going but doesnt have near the holding power as the wider forward band so use caution driving this way though it will get you by. The easiest way to verify this is what is going on is to remove the lower pan and look just past and above the small narrow end of the filter towards the passanger side of the car and straight up in the trans case there is a windowed section where you can see this band and the apply pin on it and you will likely find the band lug broken and bent or you will find a roughly 1" piece of the broken band laying in the pan when you remove it. Unfortunately this means a rebuild as the band is almost the last part that comes out of the case.
