My automatic transmission is stuck in one gear...help please.

Either two things, your reverse gear is stuck or damaged. I bought a Honda with your exact symptom and fix it. I`d replaced two gears to get it going again. If you check your tranny dipstick and find metal particles, just give it up. It`s internal problem.

Regarding the part where it won`t up shift, I`d figured that on out. The shift valve was clogged with metallic debris. I sanded that one down. Rick

Do not overlook the simple, first. Check the linkage to see if it has become loose and slipped on its adjustment. Wouldn't it be nice to find the linkage adjusted to only reach 1st gear? HTH & good luck. s

That's right. On my Honda, removing the linkage cable would make it shift to second, third, fourth faster. If I were him, I would just pop off the linkage at the tranny just to see what happens.

And when my reverse was gone, it won't upshift. The upshift valve is a mile apart but the debris that made the reverse stuck, somehow migrated to the shift valve.

On that note of keeping it simple, make sure the fluid level is correct. Also, make sure no electrical connectors, or any other connections (like vacuum lines) are loose.