2003 SS 112000 miles, seems to have. transmission making a whine when under load, just starting off, accelerating, directly related to amount of power applied, quiets when acceleration drops, not a new sound used to think it was power steering pump but replaced that, water pump and belt tensioner

felt it may have slipped accelerating up some steep hills
never had any thing done, fluid seems clean no major bubbles or burnt smell

thoughts on when I should expect it to go, what maintenance should I do to keep it going, what it might cost to replace, rebuild

hear they are expensive

 

If you truly have a "Transmission whine" it can be due to any one of several different things.
My 2000 SS had a whine about 8 years ago at 85,000. Took it to the dealer who said they found metal shavings in the pan and the transmission needed to be replaced. They did a filter/fluid change, but the whine was still there. Had no slipping so I continued driving it figuring it would die soon. At 110,000 I did my own trans. service with Mobile 1 synthetic trans. fluid and the whine went away. It now has 130,000 on it and has no whine or problems.
On the other hand, if you have slippage, that's a problem that could be caused by a few different things depending on when it slips (What gear, RPM's, more than one gear, etc.) Could be you need a new PCS (Pressure Control Solenoid), or shift solenoid, and/or a shift kit that can be done w/o removing the transmission through the side case. Do you have a CEL? Codes? I would suggest a trans. fluid and filter change with good synthetic fluid to start and look for metal filings in the pan.
As for replacement the cost can vary depending on what you replace with -Used from a junk yard $500, rebuilt $800-1000, re-manufactured $1,300 at Rock Auto, up to $4,000 for a performance transmission, plus labor if you have a shop do it. I replaced the trans. myself in my '03 SS with one from a junk yard with 110,000 on it about 4 months ago and can tell you the '03 SS trans. is a "One off" year (Other years won't work).
In summary, I would change the fluid and filter (No flush) and drive it until you get a code. If it's get bad enough it WILL throw a code.

 

I also suggest dropping the pan and doing a filter/ fluid change. If you drop the pan and see a ton of metal I would look into replacing it in the near future. I recommend Dave at TRipley edge performance to do the rebuild. He can build you a trans for stock power the whole way up to a trans capable of holding 500whp depending on what you want and how much you want to spend. His customer service is wonderful and he knows his stuff for sure!

Best of luck to you man!

 

i also recommend triple edge performance, cost me about 2100 bucks i believe and thats with the labor the shop had to install but i also had to get new axles so it might be cheaper, but i got mines done in feb. of last year and its been driving smooth every since....minus the small issues ive had (not trans related)