Your Best bet on Sundays are the Kyle, Gairloch, Ullapool, and there are Stations Open on the other side at Lairg and Dingwall. Scourie Further up opens between 12 and 2pm, and fuel at Altnaharra Hotel can be got in exchange for a major limb or Kidney
Kinlochewe most definetely closed on Sunday's and at 5 or 6pm Mon -Sat
speaking from experience on this one Alte Wolfe and I had an interesting run from Gairloch to Ullapool as a result,we were running on fumes at the end of it
The Spar Store petrol station is open on Sundays year round but I'm pretty sure only from 10a.m till 4p.m. As said previously, the main garage at end of village not open on Sundays.