PTA 325 Shifting Problems

[IowaLeatherman]

The Allison transmission in my 325 doesn't want to automatically shift/no power. We parked it in the shed last fall, ran great and this spring brought it out to use it in the field and the tractor acted like it didn't have the power to move. I checked the fluid level, was full. Can't find anyone that wants to attempt to even look at it. I talked to Big Tractor and they thought it might be a governor adjustment, but it worked fine last year before we put it to bed for the winter. Where is the first place I should be looking?