The problem:
When I let off the gas from anything over 2000 rpm the rpm drops to the point of stalling the motor.
I have cleaned the carb twice and replaced the TEV diaphragm and spring.
Mods:
Raask exhaust
K&N slab filter
!50 main jet, 55 pilot jet
Dial-a-jet (thus the 150 main jet instead of a 152,5 or a 155)
2/3 spacer mod
Idle mixture screw is 2 1/4 turns out, and very difficult to get just right as there seems to be a large range between too rich and too lean.
Raptor petcock

If I set the idle up to 1200 or 1300 rpm the stalling problem is greatly lessened, but not eliminated.
It does not happen if I leave the choke out one notch, but the engine runs poorly after it warms up.
I am stumped and would appreciate any suggestions gratefully.

Hey Artteacher, I have exactly the same issue as you

BUT

I have learned to live with it...  

My idle is set to 1200rpm, which may sopund a bit high but it helps with the dieing out issue and still makes for a nice gurgle blurble when I let off the gas when slowing down.

When the engine is still cold, I will blip the throttle when downshifting from 2nd into neutral, or simply slow down until the engine is at around 1500rpm and simply pull the clutch slowly and allow the engine to drop to idle naturally, by itself.

Since the last major job (yes, I know, pics! we want pics!   ) the Savage has died out only twice, and both times during "anticollision maneuvers"

I had this issue then discovered a mild exhaust leak, haven't had it since resolving the leak.