[B2C2]

when I first got my T337D, I had the same issue. Worked fine on the ground, did not work in the air. Finally figured out that the negative air pressure over the back of the plane was causing the gear to sit a little bit further away from the switches. The adjustment procedure in the manual did not get them quite in the right position. My mechanic adjusted the switches to be in slightly further compression on gear up and this solved the problem. Also make sure to top the hydraulic fluid after using the mule as suggested below. Otherwise you may have issues raising the gear after the testing. Had this happen after annual several times. Now I remind my A&P to top it every year.