Could my tranny be causing a loss of power?

[cmyc5575]

Hello, 83 gmc short box. 350ci backed by 350 tranny with 2500 stall.

This truck is about to drive me crazy, I have no take off power, It seems like I have a 4 cyclinder underneat the hood, its that bad. High revs before it will finally shift into second. Weird experience here lately has been when im crusining @ 60 mph the truck will all of a sudden start reving really high and seems like someone has put the truck into nutral. So, I even tried putting into first gear at the bottom so i know for sure it would be the right gear to take off in and it seems to help once in awhile, or not at all. Im thinking that Im either about to replace the torque converter or i may be losing the tranny in it. Thanks for all help upfront guys!!!