Hi, I'm Cam. May I ask your first name? I am working to get you a fast accurate answer. About your vehicle, what is the colour and condition of the transmission fluid?
The brownish is bad. THat means something is slipping and your comment on the noise does not sound good either. I suspect you have something going inside, sprag clutch or something. If the rest of the truck is in good shape then I would put a rebuilt trans in, they are about 2000 from GM and have a 3 year, 100000 mile warranty.