When im at 1/2 or above, it shifts fine into second with a nice firm shift. but going into 3rd, about 75% of the time it slips and the engines just revs.. i left off the gas, press it again, does the same.. but when im accelerating normaly it doesn't slip..

any clues? sticky valve body?

 

700R4?


Mine did this at wot. Only thing I did was take it apart and reduce the 3-4 clutch clearance down from stock specs to .040 and it solved the problem. A transgo 2&3 kit might help without taking the trans completly apart but the real fix would be both of these.