Random Idle problem

[70c10stepside]

So, a few days ago. After not running the truck for a few days this came up. After it running spot on no issues what so ever prier. It'd rev at 800-900 perfectly, in park. Slap it down in gear and it'd die out. Just wouldnt do snot. Idled it up to 1100 or so, still would just die out. So picked up the a little tranny fluid, knew it was low, and that didnt help any. Advanced the timing and it sorta helped. If the motor isn't up around operating temp it'll still die out.. But if its up around the right temp it'll run perfectly at 500-600. But. Still doesn't do much in reverse, still stalls out there regardless. Advance the timing more???

Gm hei, 355, pretty high cammed 313 duration, 750 holley, 10:5 compression(around that, have to run premium), 2200 stall, turbo 400, 4.11.

All fresh, not even 300 miles probably.

Don't know exact timing, dads a mechanic but is getting me to attack stuff now lol