Syncros in trans?

[Mustangking1]

Hi,

My mule gear selector slips out of gear while driving in either high or low range.

It also takes awhile for high range to engage.

The previous owner told me that he had the syncros replaced before because of the same problem.

Where are the syncros located, how do I tell if the syncros is bad? where can I buy them if that is what is wrong

Thanks!

Any help is greatly apprieciated!