Transfer case, transfer case actuator, and transmission question

okay lately i have had problems with my 4wd actuator f-ing up, last night it shifted into 4wd by itself going down the highway after i shifted into 2H, i got check engine codes for the 4wd actuator malfunction. how do i change out the actuator, are there any guides?

also is there a better transfer case i can put in if i have to rebuild it, i cant do a dual transfercase set up cause i have an automatic tranny

also where in NC can i get a broken not rebuild transmission and transfer case for an auto 4spd 6 cyl taco, will ones off certain 4runners work?

i can rebuild them at home and put in performance clutches, i just need some time and dont have another vehicle to drive

and btw taco hit 250k miles today