Costco stock has been stuck in the mud despite continued sales momentum.Costco Wholesale (COST 2.70%) continued its streak of strong results when it reported its fiscal Q1 earnings, but its stock, nonetheless, remains stuck in the mud. It's now trading down nearly 5% year to date and is about 11% lower over the past year, as of this writing.Below, I'll take a closer look at the retailer's results and prospects to see if the stock can break out in 2026.Strong momentumCostco's momentum continued in fiscal Q1, ...