the transmission in my 96 3/4ton 4x4 takes 2-4 seconds to engage into 1st gear when manually down shifted from 2nd. The transmission seems to shift fine in all other gears. Any ideas on what causes this and if there is a something worse to come?

Probably nothing wrong. All transmissons are prevented from going into low above certain speeds and even at lower speeds thay have to release other gears to prevent bindup.