TH400 shifting problem

[sgt1022]

Ok guys, it's been awhile since posting. I have recently run into some problems with the TH400 in my 71 c10. It's not the original tranny, but the same kind that was in the truck when I bought it. The current one is a replacement from FTI performance in Deland, FL. It is just about 1 1/2 yrs old. It recently started shifting differently/highrer that normal. I found that the hose tot he vacuum modulator came off. I replaced the modulator, hose and line to the manifold. I checked manifold vacuum and it fluctuates between 10-12 inches of vacuum. The tranny shifts from 1-2 at 4300 and 2-3 at 4100. Which is about 1500 more than normal at regular acceleration. It won't hold in any particular gear, ex. if I'm below 3000 it'll downshift to 2 from 3. I cant shift it manually through the gears. If I'm in 2 running at 3500 the tranny won't shift into 3. I am at a loss. There is plenty of fluid, all vacuum ports are closed. everything is new from the intake manifold to the modulator. I even adjusted the screw in the modulator out some. no change.