Buick Century automatically downshifting

I have 95 Century with a two month old reconditioned tranny that appears to be downshifting to third gear at around 60 mph, usually on a slight downgrade. Shortly after this started happening on a more
regular basis, I also noticed a 25% decrease in fuel economy. (It is due for an oil change and maybe new spark plugs, so perhaps the lower gas mileage is just a coincidence.) Does this sound like a major tranny problem....??
Thanks, Clueless in Texas
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Yes, not normal, get it back to the trans shop, must be scanned with a trans function scanner.

-
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Well, I just got my car back from the tranny shop, and they replaced the solenoids, and what do you know......it's still having the same problem. After driving on the freeway for about 20 minutes, it will suddenly downshift to 3rd at speeds anywhere from 50-65 mph and then gets stuck there until I pull over and turn off the engine. After that it will shift through all the gears including OD, but then as soon as I hit about 55 mph it'll downshift to 3rd again. No wonder I started using 30% more gas....driving at 70 mph in 3rd! According to a GM service bulletin, it's a valve body issue, but the valve body was replaced about 3 months ago. So it's back at the shop......
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.