All gears work fine, but will not shift into overdrive?

[Boston01X5]

Hey guys,

Transmission has been running good, no problems lately. A few days ago I noticed when I was doing about 70 on the highway the RPMs stayed around 2600 or so.

All other gears are working and shifting fine, the only problem is when I am on highway it does not go into overdrive. Prior to this the overdrive worked fine and I forget what the RPMs were at 70, but I know they were lower than 2600.

If I put in manual shift mode I can shift through all 5 gears, but it does not show overdrive.

Any suggestions where I should start?

Thanks very much for any input,

Erick