2nd gear slip

The front band applying (clamping down on the front clutch drum) is what gives you 2nd gear so it's either out of adjustment or the apply servo is leaking and not putting enough pressure on it to hold it tight. First thing I'd do is check the front band adjustment. I don't know what band apply lever it has in it so I can't say the exact proper setting but I'd try torqueing it to 72 inch lbs and back it off 2-1/4 turns. That's a good middle of the road setting. Make sure when you tighten down the locknut the inner adjusting screw doesn't turn. If your not familiar with how to adjust the front band go to YouTube and type in torqueflite front band adjustment and numerous video's will pop up. If it isn't the band adjustment I'd guess it's probably a blown seal on the front servo