dead clutch
 

I have an 88 gxl with about 100k on the engine, unknown on the tranny. Lately, it seems the clutch is slipping in 3rd and 4th at about 3500 rpm. It seems to go away after about 1/2 hour. Clutch fluid is ok, but a little black. Is my clutch dead? I do daily drive and take drifting on track. Thanks guys.

Yup, sounds like time to replace the clutch. I recently did in my GXL, and an OEM spec clutch kit (clutch disc, pressure plate, and throwout bearing) cost me about $150 around 15K on it and it's worked fine.