If the main problem is backlash in dec. you could try only guiding in RA. It is one of the options. You may be able to get long enough out of it.
If the star is wandering in RA, and the communications are all working, the possibilities are that the star is not bright enough, so the SNR is too low, or that the errors in the drive are just too large and random to allow guiding to work. I have this issue with my ancient Fullerscopes Mk.IV mount.