Transmission taking awhile to engage

[86customdeluxe]

i have a turbo 350 transmission, every gear takes awhile to engage. Having me to rev the engine so it will engage.. but after awhile or maybe a drive around the block i can park it and crank it back up and then works like "gold" literally. and fluid is perfect, im gonna change the gasket and filter ASAP, im sure it needs it. but if thats not the fix then what could it be?

hoping my transmission is not failing, i would rather pay a costly bill to get it repaired and not have to replace it.

please share your experience with me on this issue!