96' Ranger with 3.0 liter.
On colder mornings, when I turn on the ignition switch to start the engine, the starter motor turns but does not engage the flywheel to crank the engine. This happens sporadically but more frequently as the weather gets colder. I replaced the fender mounted starter solinoid but the problem still remains. Do I need to replace the starter?

probably. only other thing might be bad ring gear on the flywheel, but you can check it when pulling off the starter

On some starters, I have seen the contacts on the starter itself worn out. Will not get good current and amperage to engage fully. Some are easy fix with file, and clean up. Others are not so easy.