545rfe won't shift out of 1st

I'll see if I can describe the fault better, it launches normal to about 3000 RPM and about 25mph. Then the engine shuts down to idle and I can limp it home. As soon as it faults to idle and I let off the throttle it feels like the transmission free spools. If I wait a second or two I can launch again and repeat. The speedo is GPS so it doesn't come into play.