Stalls get their rating off a given torque at rpm, but if the torque drops, so will the "stall" but it shouldn't drop that much. You also mention the earlier shifting. Have you checked your throttle pressure linkage (kickdown) to make sure it's rigged correctly? If that's out of adjustment, early shifting can be one of the results...but it usually doesn't just suddenly lose adjustment unless it fell off the throttle linkage.
