TH350 noises, please advise

[MountainGoat1966]

83 C20 with a non lockup TH350.
Transmission was rebuilt for the previous owner of the truck and now I am dealing with the aftermath.
It shifts fine, doesn't slip, and the fluid is not burnt.
However, recently it started making whirring and whining sounds upon the engine starting and the tranny innards begin to spin.
I suspect the rebuilder did a slipshod job and did not replace the bushings and sprags.
Possibly a bad sun gear ?
I need to rebuild it myself, as a shop is totally unaffordable, even if there was one I could trust.
Any tips and advice on doing a rebuild would be greatly appreciated.

[69heavychevy]

I rebuilt my th350 last year in my tiny garage. Get yourself a good manual. Most people tend to recommend the Ron Sessions book, I personally bought the one by Cliff Ruggles only because I got it for cheap on ebay.
Do your research first before you decide to take on this task. There is plenty of info on the net to help you out. There is very good video on youtube by Hiram Gutierrez that covers a th350 rebuild. Also consider looking into some of the cheap upgrades that can be done.
I would also recommend you have an ample work area, makes it easier to lay out the parts and keep track of them.
Tear it down before you start ordering any parts, you might need more than just a clutch kit. Its a good idea to order the most complete kit you can get.
Cleanliness is key, luckily I had access to a power washer and parts washer at work so that helped out a lot.
I also had access to an arbor press at work so that made clutch and bushing work a breeze. Might be able to improvise if you don't have access to a press.
I ended up spending about $400 on parts alone for my rebuild. It included high energy clutches, complete bushing kit plus extra bushings for mods, complete seal kit and filters/screens, clutch spring tool (some people make their own), 4L60 center support, HD sprag race, new sprag, correct speedo gears for my combo, case savers, assembly lube, and trans fluid. I'm sure there's other small things I'm forgetting.
It can be done for a lot cheaper but I wanted to do it right and do it once. This was my first time ever rebuilding a tranny, and it was easier than I thought it would be.

[MountainGoat1966]

I have a parts washer with solvent, a pressure washer, 20 ton press, tons of mechanic's hand tools, and I can make the spring compressor from materials laying around here. The kit I am looking at has new bushings and sprags. I am concerned about staking the pump bushing and not screwing it up, and how to determine what other parts are worn and will need replacing.
I depend on the truck to haul my domestic water since I am remote and off the grid, and downtime is a major concern. Parts and tools I need will have to be ordered in and picked up at the post office (a three hour trip). The main reason for my post is to help determine what is causing the whine/whirring noises so I know what parts to buy, and any additional tips to make a solid dependable transmission.
The engine is a stock GM Goodwrench 350, so it's not a high performance racing application. But it needs to hold up hauling heavy water tanks on rough roads in bad conditions.

[69heavychevy]

I'm not a trans expert, but from the little I know a whirring noise usually points to a bad torque converter. Whining noise is usually a bad pump. Wouldn't be a bad idea to make sure the torque converter is fully seated on the pump.
Hopefully some trans gurus can chime in.