1993 Chevy Silverado Dropped gears

I seem to have lost some gears in my transmission. Reverse is still perfect, 2nd and 3rd are good, but first, fourth and overdrive are gone.

Is this a valve body problem ?

I am manual shifting between second and third because starting in third is extremely slow. Feels like a slipping clutch IF this were a manual transmission.

Thank you kindly

Rick