A clutch will slip first, and slip most, when it experiences the highest torque requirements. A clutch is required to transmit the most torque when the transmission is engaged in the highest gear (such that the clutch turns slowest).

In other words, you'll first notice a slipping clutch in 4/OD, then 4th, then 3rd, then 2nd, etc. By the time your clutch has begun to slip in 3rd, the car should have long since limped to the garage for a clutch-ectomy.

If you really have a slipping problem, I'd guess it's the OD which is called on to transmit higher levels of torque in lower gears (because the tranny multiplies torque in lower gears).

If you replace the clutch, be sure to also replace the rear main engine seal.

Don Foster (near Cape Cod, MA)