c4 transmission problem

I have a 66 mustang with a 3speed c4 automatic transmission and recently my transmission went out. It was driving fine on the interstate and then i hit a 2 hour traffic jam and about 15 minutes
after that (after another small jam) it would no longer go into first gear. Now the car will only drive in when in reverse. Any thoughts on the problem?
Im stuck in KY with a car that wont get me home. So any help soon would
be greatly appreciated.
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