Hello every one I have an IH 584 that won't move in any gear except the lowest gear and then it's a painfully slow creap. Its the same for foward and reverse. It has a loader on it that will still works great as does raising and lowering an extremely heavy box blade. I don't think it is sticking breaks as it seems to roll just fine on a hill out of gear. I replaced the hydro fluid and filter with no effect. So am i correct in believing I can assume it's the transmission? Thank you in advance.
Lowest gear on range (Hi/LO/R) or speed (1234) side? Those only have a mechanical transmission with no powershift that I have ever seen. Will it pull load in what it will go in? If so, its likely a problem in the shifting mechanism. They would get sloppy like the larger 56 and 66 series tractors and be difficult to get into gear. Under the cover over the center between your legs are the shifter levers and rods. See if they are moving correctly. CaseIH website has a full illustrated breakdown of the tractor available.