Refresh rate problem

Hi,
I've got a riva tnt2 model 64 video card. AMD 400mhz processor. VIA - MVP3
mb. Iiyama A701G/GT, VisionMasterpro 400 monitor. Win 98se. 128 mb memory.
I recently updated the tnt2 driver to 45.23. Now I find the computer is
alternating between allowing me a refresh rate max of 75hz and up to 100hz.
I use it at 1,024x768. So the next time I switch on the machine it will
*usually* come up at 640x480 at 75hz max. I can then can then set it to my
preferred settings of 1,024x768, 85hz. Then on the next boot up it will
come up at 1,024x768 but only a max available of 75hz.
I have tried removing the 45.23 driver and using a few utilities to clear
out any remaining stuff. But, on trying to go back to the old drivers I was
using it is not possible to get above 640x480 16 colours and 60hz refresh.
So that leaves me no option but to put back the 45.23 driver. When windows
(98se) boots up for the first time after deleting 45.23 it asks for VIDIA
Compatible Display Driver Disk 1. I know this is listed in the .inf but
don't understand what that's about.
Anyway, please, anyone know how to solve this annoying refresh rate problem.
Thanks in advance.

David