98' not shifting..

[samjoness]

I have been having an issue with my 98' Isuzu Hombre for a couple of months. It first started when it was late at night and really cold, it wouldn't shift easily. One night I was driving and the clutch was totally gone. When I pushed the pedal in, the clutch wouldn't disengage and the pedal was loose. So the next day I took it into a shop and the mechanic insisted that it was the slave cylinder. I believed him and got the slave and master cylinders replaced. The pedal felt better, but the shifting was still VERY difficult when it got cold out. Then I started having trouble after driving it for two hours straight; I couldn't shift it even if the temperature was warm outside. However, if I let it sit around over night, it was fine. I took it into another shop and they suggested just a transmission flush (which I haven't done yet due to lack of time). Since it has warmed up outside I haven't had any problems until the other day. It was driving fine, the all of a sudden it wouldn't shift, at all. It wasn't just hard, it was impossible. Even when the truck was turned off I had problems, which had never happened before. When the truck was off I put it into reverse to at least put it in a parking space, and it went forward! I was able to get it into first gear by turning the truck off again and forcing it into gear. I let the truck sit there overnight, and now it is fine. It shifts well, and goes in the right direction. I thought I just needed a new clutch, but now I am a bit worried about the transmission. I would really like a suggestion or two about why you think the problem may be.
Thanks!