I have a friend with a 95 camaro that's been in storage for a while, and now overdrive doesn't seem to work. It's always turning 3000 RPM at 60 MPH whether in D or OD, I know my car is just under 2000 RPM in OD. Shifting between the two gears does nothing, RPMs stay the same, there's no "jerk" as it shifts, and no clank or gear grinding that might indicate a problem. There are no warning lights on. Anyone have any thoughts?

 

Does his first gear work?
When my 2-3 shift selenoid went out, it caused a loss of 1st and 4th (OD) gears.

 

I don't think that was the problem but it did fix it He tried shifting into 1st and 2nd and it did appear to be engaged different gears correctly, but ever since then OD has started work, maybe something was stuck after sitting for a couple monthes?

 

Sludge and other particles in the valve body might do it. You might consider flushing and changing your transmission fluid and filter.