I have a 1989 6cyl YJ with a manual transmission. It shifts flawlessly and the clutch feels great until it has been driven for awhile. After coming to a stop, it is tough to put it into either 1st or 2nd gear. I have to put it into 3rd or 4th, then slip it into 1st. Can this be corrected by changing out the tranny fluid to the better stuff or is it a synchro issue.