I am having the same problem. I found the answer at Rock Auto.
3160 LGX 3.6 liter manual trans "clutch kit" $250.
Then there is the pressure plate for $133.00
This is the OEM clutch. I have an Edelbrock Supercharger. My current OEM clutch lasts 45mins until it slips with the same symptoms you are describing. It was damaged by a previous installer who hired a con artist. I ran a background check and what I found on Darrell R Darnell was outrageous.
33 convictions. Fugitive from justice. No ASE certifications. He screwed my car all up. With 6.9k he fried what was left of my clutch. I have the same engagement issues. 6" of dead space and either the clutch is in or out at the very top. Then if you watch your trans temp guage it will start to slip after 30 mins of use or as soon as the temp goes over 120° to 170°."clutch overuse information". Also, 1st to 2nd is like shifting into a bowl of mashed potatoes. The engine reduces power so the clutch will engage. Either way its shot and needs replacement.
It is in stock at Rock Auto with a 1 day ship delay. and I am having mine shipped directly to my shop. New shop Master Mechanic keeps "waiting on. Delco". Well, may car has been in a shop or hobbled since 07/15/2021. I'm tired of it being in the shop.
I am done waiting. He is going to install an OEM clutch. It will hold up to 600 lb ft and 468 RWHP according to GM and my installer. But using it sparingly is obviously recommended. Just go to Rock Auto or GM parts direct. *GM parts direct will not accept refunds.
www.rockauto.com
Hope this helps my six-er brothers. The S/C is tuned and now delivers 448RWHP on 93 octane. 410 on 91 octane. But if the clutch slips there is not much use for a tune.
I hope this helps.
camroChris