Transmission downshifting???

[cur.bill]

I just installed a 3.55 rear in my 1993 F350 7.3 diesel with the eod transmission. It ran fine before and runs fine now. However as I tried to bring it up to speed ( I got to 45 ) when the tach when all over the place and the trans started to downshift. I tried it a coupla times with the same outcome. The prior rear was the stock 4:10. I am stranded 200 miles from home and there is no way I will be able to drive this puppy on the interstate to get home. Is there something I can do or have a screwed up something that I am not aware of. The rear came out of my 90 F350 and I know the gears only have 3 or 4,000 miles.:

 

[MUDKICKR]

the computer uses rpm and speed to know when to shift. if there is conflection info then the trans doesnt really know what to do. also where the computer only drives the transmission it makes it worse. you will prob have to have the speedometer recalibered to run that gear ratio. any ford dealer can do that, which they charge about 1 hour labor. where are you broke down at? if your close to wv i have a 4.10 rear axle.