I was having the same problem, with Synchromax that had been in 10K miles, over a week's time it became unbearable, and I changed to Redline D4 ATF, was better initially, but then similar. Then had the car in the hills N. of LA, cold compared to PHX, and the next morning, it felt like single weight gear oil was in it.
I called RL tech support, Dave. He suggested it is a clutch problem, that it's not fully releasing, probably due to air or moisture in line (makes sense based on the symptoms.) I'm not sure when, if ever, the clutch has been bleed and flushed. I did that last night, refilled with Motul (be sure to use a pressure bleeder, or you'll be using an oil can from underneath to refill as the system got air locked -- search on bleeding the system), and based on a test drive then, appears to be fixed. I'll know more later today.
I did notice the clutch pedal seemed light recently, now it's firm again, firmer period. And had some drivetrain shudder when slipping the clutch on hill starts.
UPDATE: Yes, that was the fix, gearbox and clutch operating like when I bought the car. I like the D4 ATF, considering it's dead of winter in Phoenix, as it warms up, it provide the right blend of directness and buffering (?).
Last edited by AlanAZ; 02-02-2011 at 12:17 AM.