With the Cheetah RMVB, the low/rev band is NOT applied in "1". Only elements applied are the forward clutch and the over-running clutch is holding in "1". If it is slipping in "1", I might suspect that the over-running clutch rollers/springs have started to "lay over". The forward clutches are applied in ALL forward gears, so if the clutches were slipping, it would in 2nd and 3rd. The over-running clutch free wheels in 2nd & 3rd, so you would not notice slipping in those gears. More analysis needed to pin point, may include dropping the trans. If the over-running clutch is starting to fail, you are inviting an explosion of the direct clutch drum. Easy place to start - drop the pan and look for metal shavings.

John