A supercharged engine has so much torque off idle all the way through your rpm range that you lose torque with a high stall converter because of slippage! its not like a naturally aspirated engine that's torque comes in at say 2800 rpm and you have to rev to 2800 rpm with a trans break and a 3000 stall converter to use the torque efficiently to get a good launch !
A 3000 stall converter is a judgement measurement of the manufacturers on usually break stall at a predetermined torque, but flash stall of a converter is a different story!!!! A 2000 stall converter that might flash stall at 2500 rpm (1to1) with 350 pounds torque instantly Flashed (applied to it , a drag strip launch)! But with more torque the same 2000 converter Might flash stall at 3500 rpm with 450 Pounds of torque applied instantly with all other conditions remaining the same!!!
So when your supercharged big block applies all its torque in a flash(
) your 4500 convertors impeller and turbine rotation cant catch up to matching RPM (or reach 1to1) so your engine rpm peaks out really fast (like your "clutch is slipping" as Cobalt said) and when you speed shift to the next gear the converter is still slipping and your torque cant be used its power is eaten up by the converter (like a parasite) and the engines revs fast again with no gain of power!
I hope that helps you understand what Cobalt and I are saying! He gave you really good info!
Hes also right about the gears you don't need the big gears to get you a good launch with a good supercharger set up and the 850s sound about right ( its better to run a little rich) I ran 33 lbs boost with 2 950s on a small block 355 with 5 to 1 compression ,a 4 speed and 456 gears, 10.3 and 133 mph at the top of the quarter I was in my peek rpm range in the top of 4th gear!! If I was in the bottom of 4th I would have gone to 4.88 gears or run shorter slicks
Your cam with the big lift and overlap can be robbing boost and your cam advanced or retarded can rob more? I ran "Blower Drive Service" racing cams designed for their blowers and configurations! And their tech. people were good! But many cam company's grind good blower cams!
If you need formulas to figure out top rpm at the 1/4 mile,tire size, gears,speed Etc. just ask on here Cobalt , myself, and others on here can help you!
I reread this and hope it makes sense to you
If I made an error in it someone will correct me LOL