3550 read speed problem!

Hi, I have problem with reading discs after burning. My DVD writer is NEC 3550 and after burning disc (at any speed), reading speed falls down on 2-3mb/sec. I tried everythig, from reinstalling whole system, changing cables, deinstalling NERO… But nothing helped. Helps only system restart. After restart read speed is normal, about 8-18mb/s. So I’ve tried everythig, and finally changed DVD for NEC 4570. But NOTHING CHANGED!!! So if anybody knows solution, please help me! My computer is Intel PIV 2.4, 512MB, Mainboard is ABIT. DVD is secondary master on 80-pin cable, and DMA is on.