2003 H2 Tranny Hard Shifting

[H2mudder]

I everyone, I have researched around a little but still not sure what the problem is. My tranny is having trouble shifting from 1st to 2nd and into 3rd, it will not go into overdrive. It will not manually shift out of third into overdrive. I checked the tranny fluid and it was a little low, so I added the correct dexron III as in the manual.

My first thing i was planning on doing was changing out the tranny fluid, but would like to put my money in the right place instead of wasting money on things that will not correct the problem.

I hope I don't need to replace the tranny and it is a TPS issue or something like that.

Any suggestions would be greatly appreciated.

Thanks in advance for your comments and support.