How it reverse? Most likely there's some direct clutch or slip ring concerns. Pull the pan and look for trash in the fluid. You could do an air check but if this is the original tranny, just pull it down and see what you have. You've ordered my video which will show the things to look for.
Ken Collins, BadShoe Productions, How To DVD's specializing in Ford drivetrains www.badshoeproductions.com (banner ad below)