Built transmission?
 

Does anyone have experience with a built manual transmission? Something that can handle around 300 foot pounds of torque?

Stock will be fine. Don't dump the clutch or do any no lift-shifts. If it does take out a gear, spares are $300-500.
GEN2 trans fits in but hasn't been thoroughly battle tested

Maybe so, but that’s not the whole story. I have a Jackson racing supercharger already with the high boost pulley and the E85 conversion from Delicious Tuning. My supercharger died and I got a replacement and it doesn’t make as much power as the old supercharger did. I’m planning on upgrading to a.Sprintex 335 which makes a lot more torque, especially at lower RPMs. I recently upgraded to an Exedy stage one clutch and stupidly put Amsoil gear lube in the transmission. After driving it back-and-forth to work for a week, it now makes a horrible noise when decelerating in fourth and fifth gear. I changed it out to Motul Gear 300 but it still makes that noise. I’m worried that the stock transmission is toast now and I’m looking for alternatives. i’m considering getting a transmission from Jack’s so I don’t have to worry about it.

The critical flaw in the transmission is with the way the 4th gear syncro functions (not the syncro itself). Jack's can do all sorts of things but if they haven't addressed this, you'll have the same weakness.
I do agree that the Sprintex 335 makes dangerous torque because it's so high in low RPM.
Keep us apprised on how it works out!

huh what is wrong with amsoil gear oil ?? I switched my gear 300 out for amsoil MTF since its a proper GL4 oil NOT a gl4/gl5 hybrid like gear 300 and its been great. Had it like this street/track for years now.

Did you use amsoil severe gear by mistake ? That is GL5 and not for our transmissions

Guys have broken the Jacks transmissions too. You really want bulletproof go CD009. Or just buy used stocks transmissions and keep a spare on hand.

This is what I got

https://www.amsoil.com/p/amsoil-75w-...?code=MTGQT-EA

Yup same stuff I been using. I just buy the bag version for easy fill
https://www.amsoil.com/p/amsoil-75w-...?code=MTGPK-EA

Sorry you had bad luck with it but that amsoil or the redline mt-90 is really good stuff for these transmissions. Do a search on here for gear300 and you will find people switching away from it.

Either way I am not sure the oil was the issue here anyway