need help again idle problems!

[72 Blaze]

ok guys this time its not the blaze. i just bought an old 2000 chevy 4x4 2500. its got a 454 and it has a crazy idle. sometimes it runs great and other times it still runs good it just idles up and down up and down when i come to a stop. seems to be after it gets hot.i unpluged the throttle what ever it is sensor and no change. its got a brand new trans really i bought it from the trans shop. so i have been the first to drive it. it shifts great. i was told it could be the torque converter trying to lock up. any ideas???

and as always thanks for the help!!