Run out of ideas about motor skipping solutions. Request for more ideas...

Hi,

I'm having trouble with stepper motor skipping and have exhausted my list of 'what to do about it'. So, I'm looking for any ideas

I'm printing a long thin plate (100mm by 30mm - 5mm high) - if I print it long on x-axis then I get layer shift on every layer (x-axis shift only) . However, if I print it long on the y-axis it's perfect (i.e. no layer shift on x or y-axis). So, I believe my printer is skipping steps on the x-axis (only) when that axis is 'under load'. Printing small (e.g. 20mm square ish) objects works fine too.

I've tried
- turning the x-axis trim pot up and down (motor got hotter or cooler but but layer shift still occurred in both cases)
- adding fans to cool my GEN6 board (heat sinks now cooler throughout print but layer shift still occurs)
- adding fans to cool the x-axis motor and extruder motor (motors now cooler throughout print but layer shift still occurs)

(I also checked the x-axis belt pulley to check it wasn't slipping and causing backlash - though I believe I'd get layer shift when printing long on y -axis then too)

Any ideas what to try next?

Many Thanks

Pete