2007 Ford F150 5.4L Engine Miss Fire: P0301 & P0316 Codes, Cold Start Issues

Hi everyone, I recently purchased a 2007 Ford F15-0 5.4L V8 4x4 truck three weeks ago. It ran smoothly during the first week of ownership. However, starting about a week after that, it began experiencing engine misfires only when cold. Once the engine reached normal operating temperature, the issue disappeared. Currently, the problem occurs consistently under certain driving conditions—most noticeably at around 70 mph when shifting into fourth gear and RPMs drop. The Check Engine Light (CEL) flashes during these instances, and the condition worsens significantly when climbing hills. I took it to Auto Zone with the CEL illuminated and received diagnostic codes: P0301 (misfire detected in cylinder 1) and P0316 (random/multiple misfires at start-up). I've already replaced both the spark plug and coil pack for cylinder 1, but the problem persists. Any insights or troubleshooting steps would be greatly appreciated! Thanks in advance.