loss of overdrive

1992 Buick Roadmaster Wagon : While cruising along on interstate @ 70 I all of a sudden lost overdrive.
was able to complete Journey at 55 with 3000 rpm instead of 1700.
Also didn't want to shift well from 2nd to 3rd @ 30 mph. Any ideas about possible problems and or solutions

Hit up an autozone or advanced auto parts store. See if a store/ or garage has a computer, and see whats going on.
Now when you said driving at 70, and completed at 55, did it decelerate or just stop and you couldnt use overdrive? And that sounds Like you got deep problems coming your way....
something else you can do, but i wont/dont say you should.... When it does that, Put your veichle into nutureal, keep her at the rpms you want to drive at for a second, let off the gas, and put her back into o/d. See if that helps any for the time being...
Bill