Auto tranny gurus I need help

[budgetstperformance]

ok i have an 87 crew cab dually with a 454 big block and th400 trans.
i have a problem with the tranny slippin i droped the pan and found a bunch of metal dust. no chunks. i changed the filter and put new fluid and it was working good again. i thought that it was slipping cause the filter/pick up tube had droped out of its seat cause i found it laying in the pan.

now it is slipping again, fluid is toped off. its slipping so bad the truck wont move. then i shut the truck off and wait 30 seconds and it will go for a couple blocks.

feels like the fluid pressure is low, normally when i put the truck in gear i get a strong kick even at idle. now no kick when i put it in gear.

is there any external adjustments or is it time to look for a tranny.
if i need to replace it i would like to know what year trannys would be compatible. i need to get the truck running again as cheap as possible.

thank in advance guys.