Transmission is slippin from 1st to 2nd. What is the best thing to do? on 2000 Chevrolet Suburban 1500

Could it be a cellinoid? Or do I need to replace the whole tran? Is it possible to fix without replacing? Could it be only a seal?

Asked by for the 2000 Chevrolet Suburban 1500
a couple of questions. 1 do you have a ck eng light on? 2 how many miles on veh.3 have you had trans serviced before