Engine Stalling

Just got my RV cammed, 8:1 or so CR, 454 back from the shop where they swapped out the TH400 for tremec TKO 600.
Has an old style holley 4011 speadbore which has been very reliable until now.

Was sitting in the shop about 2 months.

Idle was fine when it went in. About 650 rpm in drive, 900 neutral and never stalled with the A/T.
After tranny install, they reset idle to 850.

When i was driving it home it was stalling at stop lights.

Once in my garage it would ildle for a while (idle was set now at 850) then the tack would take an abupt nose dive like it was going to stall, but just before stalling it would come back up.
It was so abrupt that i suspected ignition but found nothing.
Occaionally it would stall in the garage but most always when driving. I removed the primary sight glass and the fuel was just ever so slightly below it...just enough that it didin't run out thru sight hole but right there at the bottom.

I checked for vaccum leaks but couldnt find any.
To be sure, i removed all vacuum lines and capped them off and still had the same problem.

Idle screws are at 1 1/4 turns out and can't adjust it out with mixture adjustments.
I reset the timing to 38*.
With the th400 it ran fine anywhere from 36-40*.

I can only get rid of it by bringing idle speed up to 1000 and then it is fine about 95% of the time, but even then it still dies once in a while.
Note that the problem is much worse with lower idle speeds but really doesn't improve until i get to 1000. Then it is almost gone (suddenly at 1000).

Any suggestions on diagnosis would be helpful/appreciated as i would like to get her idling reliably at 650 or so.

Question: With the A/T, i presume the idle speed adjustment position (650 in drive, 900 in neutral) was such that the throttle valves were open only slightly further than they were when i got it back from the shop (850 in neutral). It seems that the idle speed adjustment is now about where it was with the A/T tho the problem doesnt now dissappear until it is at idle =1000 i.e the old 900 idle wont keep her running. Is is possible that there is a carb problem and what would that be that it wont idle with the throttle valves at this more closed position?

How could something like this occur from sitting for 2 months or is something else going on that i am not seeing?